Skip to main content

Full text of "Chemical embryology"

See other formats




New Tork 

The Macmillan Co. 



Cambridge University Press 

Bombay, Calcutta and 


Macmillan and Co., Ltd. 


The Macmillan Co. of 

Canada, Ltd. 

All rights reserved 


f) ^ 


Vir PraecLarissinius 


Mysterii Generationis Indaqator Diliqens. 

Q) r^^Lji(iJ<^i~^4^(tJ^^^i~^^L3(*J<^^>^L3(*^^ 




M. A., Ph.D. 

Fellow ofGonville & Cains College, Cambridge, and 

University Demonstrator in 





3 'j>^t>r^<?>^t>r^)(r>^t>f7)(j>^t>r^cp^<jt>^ ^ 



in Univ. Aberdon. Anat. olim Professori 


Schol. Undel. olim Praeposito 


Coll. Gonv. et Caii olim Custodi 


Artis chemicae ad animantia spectantis in 
Univ. Cantabrig. Professori 


hanc suam disquisitionem 


sacram voluit 

For more, and abler operations are required to the Fabrick 
and erection of Living creatures, than to their dissolution, 
and plucking of them down : For those things that easily 
and nimbly perish, are slow and difficult in their rise and 

William Harvey, Anatomical Exercitations concerning 
the generation of living creatures, London, 1653, 
Ex. XLi, p. 206. 

That discouraging Maxime, Nil dictum quod non 
dictum prius, hath little room in my estimation, nor can 
I tye up my belief to the Letter of Solomon ; I do not think, 
that all Science is Tautology; these last Ages have shown 
us, what Antiquity never saw; no, riot in a dream. 

Joseph Glanville, Scepsis Scientifica, an essay of the 
vanity of dogmatizing, and confident opinion, London, 
1 66 1, Chap. XXII. 



Prolegomena page 2 


The Theory of Chemical Embryology 

Philosophy, Embryology, and Chemistry 7 

The Historical Perspective 10 

Obstacles to Chemical Embryology 1 3 

The Stumbling-block of Hormism 1 4 

Finalism as a Rock of Offence 1 6 

Organicism as an Occasion of Falling 25 

Organicism and Emergence 3^ 

Neo-Mechanism as a Theory for Chemical Embryology 32 


The Origins of Chemical Embryology 

Preliminary Note 41 

Section i . Embryology in Antiquity 44 

I • I . Non-Hellenic Antiquity 44 

1-2. Hellenic Antiquity; the Pre-Socratics 50 

1-3. Hippocrates; the Beginning of Observation 53 

1-4. Aristotle ^g 

1-5. The Hellenistic Age 77 

1-6. Galen 85 

Section 2. Embryology from Galen to the Renaissance gi 

2-1. Patristic, Talmudic, and Arabian Writers gi 

2-2. St Hildegard; the Lowest Depth g^ 

23. Albertus Magnus gy 

2-4. The Scholastic Period 103 

2-5. Leonardo da Vinci 1 07 

2-6. The Sixteenth Century; the Macro-iconographers I lO 

NE h 

'> i 

/ i\ '\ ^ , 



Section 3. Embryology in the Seventeenth and Eighteenth Centuries page 125 

3-1. The Opening Years of the Seventeenth Century 1 25 

32. Kenelm Digby and Nathaniel Highmore 1 29 

3-3. Thomas Browne and the Beginning of Chemical Embryology 135 

3-4. William Harvey 138 

35, Gassendi and Descartes; Atomistic Embryology 1 56 

36. Walter Needham and Robert Boyle 1 60 
3-7. Marcello Malpighi; Micro-iconography and Preformationism 166 
3-8. Robert Boyle and John Mayow 169 
3-9. The Theories of Foetal Nutrition 176 
3-10. Boerhaave, Hamberger, Mazin 1 82 
3-11. Albrecht v. Haller and his Contemporaries 1 88 
3-12. Ovism and Animalculism 1 99 
3- 1 3. Preformation and Epigenesis 205 
3-14. The Close of the Eighteenth Century 215 
3-15. The Beginning of the Nineteenth Century 220 


General Chemical Embryology 

Preliminary Note 

Section i. The UnfertiUsed Egg as a Physico-chemical System 

1 . Introduction 

2. General Characteristics of the Avian Egg 

3. The Proportion of Parts in the Avian Egg 

4. Chemical Constitution of the Avian Egg as a Whole 

5. The Shell of the Avian Egg 

6. The Avian Egg-white 

7. The Avian Yolk 

8. The Avian Yolk-proteins 

9. The Fat and Carbohydrate of the Avian Yolk 

10. The Ash of the Avian Egg 

1 1 . General Characteristics of non-Avian Eggs 

12. Egg-shells and Egg-membranes 

13. Proteins and other Nitrogenous Compounds 

14. Fats, Lipoids, and Sterols 

15. Carbohydrates 

16. Ash 







Section 2. On Increase in Size and Weight 

page 368 

2-1. Introduction 

2-2. The Existing Data 369 

2-3. The General Nature of Embryonic Growth 383 

2-4. The Empirical Formulae 389 

2-5. Percentage Growth-rate and the Mitotic Index 399 

2-6. Yolk-absorption Rate 405 

2 '7. The Autocatakinetic Formulae 408 

2-8. Instantaneous Percentage Growth-rate 420 

2-9. Growth Constants 434 

2-10. The Growth of Parts 440 

2-1 1. Variability and Correlation 455 

2-12. Explantation and the Growth-promoting Factor 460 

2-13. Incubation Time and Gestation Time 470 

2-14. The Effect of Heat on Embryonic Growth 498 

2-15. Temperature Coefficients 503 

2 • 1 6. Temperature Characteristics 515 

2-17. The Effect of Light on Embryonic Growth 533 

2-i8. The Effect of X-rays and Electricity on Embryonic Growth 536 

2-19. The Effect of Hormones on Embryonic Growth 538 

Section 3. 





On Increase in Complexity and Organisation 
The Independence of Growth and Differentiation 

Chemical Processes and Organic Form 
The Types of Morphogenetic Action 
Pluripotence and Totipotence 
Self-differentiation and Organiser Phenomena 
Functional Differentiation 
Axial Gradients 
Organised and Unorganised Growth 

3-10. Chemical Embryology and Genetics 



Section 4. The Respiration and Heat-production of the Embryo 615 

4- 1 . Early Work on Embryonic Respiration 6 1 5 

4-2. Respiration of Echinoderm Embryos in General 623 

4-3. Rhythms in Respiratory Exchange 64 1 



Section 4-4. Heat Production and Calorific Quotients of Echinoderm page 649 

4-5. Respiration of Annelid, Nematode, Rotifer, and Mollusc 659 

46. Respiration of Fish Embryos 665 

47. , Respiration of Amphibian Embryos 67 1 
4-8. Heat-production of Amphibian Embryos 682 
49. Respiration of Insect Embryos 687 
4- 1 o. Respiration of Reptile Embryos 692 
4-11. Respiration of Avian Embryos in General 693 
4-12. Heat-production of Avian Embryos 7^4 
4-13. Later Work on the Chick's Respiratory Exchange 7^8 
4- 1 4. The Air-space and the Shell 7 1 9 
4-15. Respiration of Mammalian Embryos 726 
4" 1 6. Heat-production of Mammalian Embryos 732 
4-17. Anaerobiosis in Embryonic Life 742 

^, 4" 1 8. Metabolic Rate in Embryonic Life 746 

4-19. Respiratory Intensity of Embryonic Cells fn wVro 755 

4-20. Embryonic Tissue-respiration and Glycolysis 758 

4-21. The Genesis of Heat Regulation 772 

4-22. Light-production in Embryonic Life 776 

Section 5. Biophysical Phenomena in Ontogenesis 777 

5-1. The Osmotic Pressure of Amphibian Eggs 777 

5-2. The Genesis of Volume Regulation , 786 

53. The Osmotic Pressure of Aquatic Arthropod Eggs 790 

54. The Osmotic Pressure of Fish Eggs 793 

5-5. Osmotic Pressure and Electrical Conductivity in Worm and 799 
Echinoderm Eggs 

5-6. The Osmotic Pressure of Terrestrial Eggs 8l2 

5-7. Specific Gravity 820 

5-8. Potential Differences, Electrical Resistance, Blaze Currents 825 
and Cataphoresis 

5-9. Refractive Index, Surface Tension and Viscosity 833 

Section 6. General Metabolism of the Embryo 839 

6-1. The j&H of Aquatic Eggs 839 

6-2. The j&H of Terrestrial Eggs 855 

63. rH in Embryonic Life 865 

6-4. Water-metabolism of the Avian Egg 870 


Section 6-5. Water-content and Growth-rate page 883 

6-6. Water-absorption and the Evolution of the Terrestrial Egg 889 

6-7. Water-metabolism in Aquatic Eggs 906 

6-8. The Chemical Constitution of the Embryonic Body in Birds 911 
and Mammals 

69. Absorption-mechanisms and Absorption-intensity 917 

6- 10. Storage and Combustion; the Plastic Efficiency Coefficient 934 

6-1 1. Metabolism of the Avian Spare Yolk 939 

6-12. Maternal Diet and Embryonic Constitution 943 

Section 7. The Energetics and Energy-sources of Embryonic Development 946 

7-1. The Energy Lost from the Egg during Development 946 

7-2. Energy of Growth and Energy of Differentiation 956 

7-3. The Relation between Energy Lost and Energy Stored 962 

7-4. Real Energetic Efficiency • 969 

7-5. Apparent Energetic Efficiency 972 

7*6. Synthetic Energetic Efficiency 98 1 

7-7. The Sources of the Energy Lost from the Egg 986 

Sections. Carbohydrate Metabolism 1000 

8-1. General Observations on the Avian Egg lOOO 

8-2. Total Carbohydrate, Free Glucose, and Glycogen lOOl 

8-3. Ovomucoid and Combined Glucose 1 007 

8-4. Carbohydrate and Fat 1014 

8-5. The Metabolism of Glycogen and the Transitory Liver 1018 
8-6. Free Glucose, Glycogen, and Insulin in the Embryonic Body IO29 
8-7. General Scheme of Carbohydrate Metabolism in the Avian Egg 1035 

8-8. Embryonic Tissue Glycogen 1 036 

8'9. Embryonic Blood Sugar 1039 

8- 10. Carbohydrate Metabolism in Amphibian Development 1043 

8*i I. Carbohydrate Metabolism of Invertebrate Eggs I047 

8-12. Pentoses 1 05 1 

8-13. Lactic Acid 1 051 

8-14. Fructose 1054 

Section 9. Protein Metabolism 1055 

9* I. The Structure of the Avian Egg-proteins before and after 1055 


9*2. Metabolism of the Individual Amino-Acids I059 

9-3. The Relations between Protein and non-Protein Nitrogen 1065 

9-4. The Accumulation of Nitrogenous Waste Products 10 76 


Section 9-5. Protein Catabolism page 

9-6. Nitrogen-excretion; Mesonephros, Allantois, and Amnios 

9-7. The Origin of Protective Syntheses 

9*8. Protein Metabolism of Reptilian Eggs 

9-9. Protein Metabolism of Amphibian Eggs 

9' 10. Protein Metabolism in Teleostean Ontogeny 

9-11. Protein Metabolism in Selachian Ontogeny 

9* 1 2. Protein Metabolism of Insect, Worm, and Echinoderm Eggs 

9-13. Protein Utilisation in Mammalian Embryonic Life 

9-14. Protein Utilisation of Explanted Embryonic Cells 

9-15. Uricotelic Metabolism and the Evolution of the Terrestrial Egg 

Section 10. The Metabolism of Nucleins and Nitrogenous Extractives 

[O-i. Nuclein Metabolism of the Chick Embryo 

IO-2. The Nucleoplasmatic Ratio 

[0-3. Nuclein Synthesis in Developing Eggs 

[0-4. Creatinine, Creatine, and Guanidine 

Section 11. Fat Metabolism 

I • I . Fat Metabolism of Avian Eggs 

1-2. Fat Metabolism of Reptilian Eggs 

I •2- Fat Metabolism of Amphibian Eggs 

I -4. Fat Metabolism of Selachian Eggs 

1-5. Fat Metabolism of Teleostean Eggs 

1-6. Fat Metabolism of Mollusc, Worm, and Echinoderm Eggs 

1-7. Fat Metabolism of Insect Eggs 

1-8. Combustion and Synthesis of Fatty Acids in Relation to 
Metabolic Water 

1 1 -9. Fat Metabolism of Mammalian Embryos 

Section 12. The Metabolism ofLipoids, Sterols, Cycloses, Phosphorus 
and Sulphur 

1 2- 1. Phosphorus Metabolism of the Avian Egg 

12-2. Tissue Phosphorus Coefficients 

I2'3. Choline in Avian Development 

12-4, The Metabolism of Sterols during Avian Development 

1 2*5. The Relation between Lipoids and Sterols; the Lipocytic 

12-6. Cycloses and Alcohols in Avian Development 

12-7. Sulphur Metabolism of the Avian Egg 

12-8. Phosphorus, Sulphur, Choline, and Cholesterol in Reptile Eggs 


Section 12-9. Lipoids and Sterols in Amphibian Eggs page 1237 

12-10. Lipoids, Sterols, and Cycloses in Fish Eggs 1239 

i2'ii. Phosphorus, Lipoids and Sterols in Arthropod Eggs 1241 

12-12. Phosphorus, Lipoids, and Sterols in Worm and Echinoderm 1243 


12-13. Lipoids and Sterols in Mammalian Development 1252 

Section 13. Inorganic Metabolism 1255 

[ 3- 1 . Changes in the Distribution of Ash during Avian Development 1 255 

32. Calcium Metabolism of the Avian Egg 1260 

33. Inorganic Metabolism of other Eggs 1 268 
3-4. The Absorption of Ash from Sea-water by Marine Eggs 1 27 1 
3-5. The Ani on/Cation Ratio 1 2 74 
3-6. Inorganic Metabolism of Mammalian Embryos 1277 
3-7. Calcium Metabolism of Mammalian Embryos 1285 

Section 14. Enzymes in Ontogenesis 1289 

4-1. Introduction 1 289 

4-2. Enzymes in Arthropod Eggs 1290 

4-3. Enzymes in Mollusc, Worm, and Echinoderm Eggs 1293 

4-4. Enzymes in Fish Eggs 1 295 

4-5. Enzymes in Amphibian Eggs 1300 

4-6. Enzymes in Sauropsid Eggs 1303 

4-7. Changes in Enzymic Activity during Development 1307 

4-8. Enzymes of the Embryonic Body 1 3^0 

4-9. Enzymes in Mammalian Embryos 13 12 

4-10. The Genesis of Nucleases 1326 

4-11. Foetal Autolysis 1 329 

Section 15. Hormones in Ontogenesis 1335 

5-1. Introduction 1335 

5-2. Adrenalin ^337 

53. Insulin 1342 

5-4. The Parathyroid Hormone 134^ 

5-5. The Hormones of the Pituitary 134^ 

5-6. Secretin 134^ 

5-7. Thyroxin 134^ 

5-8. Oestrin and other Sex Hormones • 1353 



Section i6. Vitamins in Ontogenesis page 1359 

[6-1. Vitamin A 1359 

[6-2. Vitamin B 1360 

[6-3. Vitamin C 1 360 

[6-4. Vitamin D 1 360 

[6-5. Vitamins in Mammalian Development 1 363 

[6-6. Vitamin E 1 365 

Section 17. Pigments in Ontogenesis 1368 

[7-1. The Formation of Blood Pigments 1 368 

[7-2. The Formation of Bile Pigments 137^ 

[7-3. The Formation of Tissue Pigments 1 375 

[7-4. The Pigments of the Avian Egg-shell 137^ 

[7-5. The Pigments of the Avian Yolk 1378 

[7-6. Egg-pigments of Aquatic Animals 1380/ 

[7-7. Melanins in Ontogenesis 13^^ 

Section 18. Resistance and Susceptibility in Embryonic Life 1383 

•I. Introduction 1 3^3 

•2. Standard Mortality Curves 1 3^3 

[8-3. Resistance to Mechanical Injury ^3^5 

$-4. Resistance to Thermal Injury 1 388 

5-5. Resistance to Electrical Injury ^392 

[8-6. Resistance to Injury caused by Abnormal j&H 1 397 

5-7. Resistance to Injury caused by Abnormal Gas Concentrations 1 399 

(non-Avian Embryos) 

!-8. Critical Points in Development 1 409 

!-g. Resistance to Injury caused by Abnormal Gas Concentrations 1 4 1 4 
(Avian Embryos) 

>-io. Resistance to Injury caused by Toxic Substances 1420 

••I I. Resistance to Injury caused by X-rays, Radium Emanation, 1 43 1 
and Ultra-violet Light 

Section 19. Serology and Immunology in Embryonic Life 1444 

ig-i. Antigenic Properties of Eggs and Embryos ^444 

19-2. The Formation of Natural Antibodies 1446 

19-3. The Natural Immunity of Egg-white ^447 

19-4. Inheritance of Immunity in Oviparous Animals HS^ 

19-5. Serology and Pregnancy 1452 

19-6. Resistance of the Avian Embryo to Foreign Neoplasms 1 454 



Section 20. Biochemistry of the Placenta page 14.^6 

20-1. Introduction 1 45" 

20-2. General Metabolism of the Placenta 145^ 

20-3. Placental Respiration 1 46 1 

20-4. Nitrogen Metabolism of the Placenta 1 462 

20-5. Carbohydrate Metabolism of the Placenta 14^9 

20-6. Fat and Lipoid Metabolism of the Placenta 1472 

20-7. Placental Enzymes 1481 

Section 21. Biochemistry of the Placental Barrier 1485 

2 1 • I . The Autonomy of the Foetal Blood 1 4^5 

21-2. Evolution of the Placenta -4^7 

21-3. Histotrophe and Haemotrophe 149^ 

21-4. Mesonephros and Placenta 1 493 

21-5. Colostrum and Placenta ^497 

21-6. Placental Transmission and Molecular Size 1497 

21-7. QuaHtative Experiments on Placental Permeability 1 505 

21-8. The Passage of Hormones 15^^ 

2 1 -9. Factors Governing Placental Transmission 15^2 

2I-IO. Quantitative Experiments on the Passage of Nitrogenous 15 14 

2 1 -I I. Quantitative Experiments on the Passage of Phosphorus, Fats, 1520 

and Sterols 
2i'i2. Quantitative Experiments on the Passage of Carbohydrates 1525 

2i*i3. Quantitative Experiments on the Passage of Ash 1 52 7 

21-14. The Passage of Enzymes 15^9 

2i*i5. The Unequal Balance of Blood Constituents 1530 

Section 22. Biochemistry of the Amniotic and Allantoic Liquids 1534 

22-1. Introduction 1 534 

22-2. Evolution of the Liquids ^535 

22-3. Avian Amniotic and Allantoic Liquids 1 537 
22-4. Amount and Composition of Mammalian Amniotic and Allan- 1539 

toic Liquids 

22-5. Maternal Transudation and Foetal Secretion 154^ 

22-6. Interchange between Amniotic and Allantoic Liquids 15^2 

22-7. Vernix Caseosa 1 5^4 

Section 23. Blood and Tissue Chemistry of the Embryo 1565 

23-1. Blood 1565 

23-2. Lung 1 57 1 

23-3. Muscle 1574 



Section 23-4. 



Nervous Tissue 


Connective Tissue 




Sense Organs 


Intestinal Tract 

Section 24. 

Hatching and Birth 




Hatching Enzymes 


Osmotic Hatching 




Hatching of the Avian Egg 


MammaUan Birth 

page 1577 





The Two Problems of Embryology 1 6 1 3 

The Cleidoic Egg and its Evolution 16 1 3 

Chemical Synthesis as an Aspect of Ontogeny 1 623 

Biochemistry and Morphogenesis 1 624 

Transitory Functions in Embryonic Life 1627 

The Theory of Recapitulation 1629 

Recapitulation and Substitution ' 1632 

Chemical Recapitulation 1638 

Provisional Generalisations for Chemical Embryology 1 647 
The Organisation of Development and the Development of Organisation 1659 

The Future of Embryology 1 664 



i. Normal Tables of Magnitudes in Embryonic Growth 1669 

ii. A Chemical Account of the Maturation of the Egg-cell 1679 

iii. The Chemical Changes during the Metamorphosis of Insects (by 1685 

Dorothy Needham) 

iv. The Development of the Plant Embryo from a Physico-chemical View- 1 7 1 1 

point (by Muriel Robinson) 


Bibliography and Author-Index 


Index Animalium 




William Harvey frontispiece 

I. Primitive methods of incubation : (A) Egyptian, (B) Chinese facing page 46 
II. The oldest known drawing of the Uterus (gth century) . „ „ 82 

III. Illustration from the Liber Scivias of St Hildegard (ca. 

1150A.D.) jj J3 96 

IV. A page from Leonardo da Vinci's Anatomical Notebooks 

(ca. 1490 A.D.) ........„„ 108 

V. Illustration from the De Formatione Ovi et Pulli of Fabricius 

(1604) „ „ 116 

VI. Illustration {rom Highmore's History of Generation {16^1) . „ „ 134 

VII. Illustrations from Malpighi: i)e Or;o in^M^a/o (1672) . ,, „ 168 

VIII. Reaumur's Illustration of his Incubators (1749) . . „ „ 198 

IX. Microphotograph of the yolk of the hen's egg at the time 

of laying, to show the vitelline globules . . . . ,, ,, 236 

X. Microphotograph of the yolk of the hen's egg, not yet 

liberated from the ovary, to show the stratification . . „ ,, 288 


The frontispiece of William Harvey's Generation of Ani- 
mals ( 1 65 1 ) ; Zeus liberating living beings from an egg . frontispiece 

XI. Microphotograph of the yolk of the hen's egg at the 
eleventh day of incubation, showing its heterogeneous 
state .......... facing page 836 

XII. Microphotograph of the yolk of the hen's egg at the second 

day of incubation, showing the cholesterol esters . . „ ,,1218 


An embryological investigation in the eighteenth century frontispiece 


27. Ash of the avian egg .... 

34. Distribution of amino-acids in egg-proteins 

47. Ash content of egg . 

195. Enzymes in the hen's egg 

199. Enzymes in the human embryo 

201. Enzymes in the pig embryo 

220. Placental enzymes . 

227, Passage of substances through the placenta 
Appendix 1, Table 3. Embryonic growth of the hen 

facing page 


»5 55 


.J 55 


55 55 


55 55 


55 55 


55 55 


55 5' 


55 5? 





THOSE who have assisted me in the preparation of this work are so 
numerous that it is impossible to mention them all by name. Its 
original impetus was derived from a discussion with Professor Sir 
F. G. Hopkins in 1923 on the observation of Klein that inositol, though 
absent from the undeveloped hen's egg, was present in considerable 
quantity at hatching; and throughout the period of preparation his 
encouragement, help, and advice were never-failing. I have derived great 
benefit from the discussion of various points with Miss Marjory Stephenson, 
M. Louis Rapkine, Dr R. A. Fisher, and my wife. Professor J. T. Wilson 
has been repeatedly helpful to me on anatomical points, and in the 
Zoological Laboratory I was always sure of obtaining expert advice from 
Mr James Gray, Mr J. T. Saunders, Mr C. F. A. Pantin and Dr Eastham. 
I have relied much upon the kindness and wide biological knowledge of 
Dr D. Keilin and Dr F. H. A. Marshall. As regards the historical chapters, 
I am most grateful to Dr Charles Singer, who annotated them with 
valuable comments, and to Professor R. C. Punnett who placed un- 
reservedly at my disposal his knowledge of the history of generation, and 
his library of old and rare biological books. To Dr Arthur Peck I am 
indebted for the correction of my Greek, and it was Professor A. B. Cook 
who guided me to the embryology of the ancients. Without the assiduous 
backing of Mr Powell, the Librarian of the Royal Society of Medicine, and 
his assistants, I should have dealt much more inadequately than I have 
with the papers which cannot be consulted in Cambridge. I have also to 
thank the administrators of the Thruston Fund of Gonville and Caius 
College for a grant which was devoted to incidental expenses. For the 
indexes I wish to thank Miss Helen Moyle, and for other services which 
have made the book possible, Mrs V. Townsend. My thanks are also 
due to the Editors of the following journals: Biochemical Journal, Journal 


of Experimental Biology, Biological Reviews, Science Progress, and the Monist, 
for permission to reprint passages from papers. I must record my gratitude 
to the following friends, who very kindly read through and criticised the 
proofs of the various sections: 

Part I 

Professor A. E. Boycott 
Dr J. H. Woodger 

Part II 

Professor R. C. Punnett 
Dr Charles Singer 
Dr Reuben Levy 
Dr Arthur Peck 
Sir William Dampier 
Professor A. B. Cook 
The Rev. W. Elmslie 
Professor F. M. Cornford 

Part III 


1 Professor R. H. A. Plimmer 
Mr J. B. S. Haldane 

2 Dr Samuel Brody 
Mr James Gray 
Dr E. N. Willmer 

3 Mr G. R. de Beer 

Mr C. H. Waddington 
Mr J. B. S. Haldane 

4 Dr D. Keilin 
Professor Munro Fox 

5 Mr T. R. Parsons 
Dr Malcolm Dixon 

6 M. Louis Rapkine 
Mr C. Forster Cooper 

7 Miss Marjory Stephenson 
M. Louis Rapkine 

Dr D. Keilin 

8 Dr Eric Holmes 

Dr Bruce Anderson & Mrs Margaret 
Whetham Anderson 




Dr Dorothy Jordan Lloyd 

Professor J. Murray Luck 

Mr C. Forster Cooper 


Mile Eliane LeBreton 


Professor J. B. Leathes 


Dr Irvine Page 


Dr Elsie Watchorn 


Dr Barnet Woolf 

MrJ. B. S. Haldane 


Dr Howard Florey 


Dr Leslie J. Harris 

Dr A. L. Bacharach 


Dr Howard Whittle 


Mr C. F. A. Pantin 

Professor A. R. Moore & Mrs Moore 


Dr John Hammond 


Dr St G. Huggett 


Dr Arthur Walton 


Dr Barbara Holmes 


Dr F. H. A. Marshall 


Professor L. G. M. B. Becking 

Dr D. Keilin 

Dr G. S. Carter 

Professor Lancelot Hogben 

Mr G. R. de Beer 

Professor A. R. Moore & Mrs Moore 

Appendix III 
Dr L. E. S. Eastham 

I am indebted to the Master of Gonville and Caius College for permission 
to reproduce the portrait of William Harvey (attributed to Rembrandt) 
in the Senior Combination Room. Finally, I am glad to record here my 
gratitude to the StafTof the Cambridge University Press for the unremitting 
care which they gave to my book during the course of its preparation. 

J. N. 

Note: The use of the shortened 
and (&) indicates collaboration 
between two or more authors. 


The Sciences, unlike the Graces or the Eumenides, are not limited 
in number. Once born, they are immortal, but, as knowledge in- 
creases, they are ever multiplying, and so great is now the dominion 
of the scientific mind that every few years sees a new one brought 
into the world. Some spring, fully armed, from the brains of one or 
two men of genius, but most of them, perhaps, come only gradually 
to their full development through the labours of very many obscure 
and accurate observers. 

If the analogy may be permitted, physico-chemical embryology has 
so far been living an intra-uterine existence. Its facts have been 
buried in a wide range of scientific journals, and its theories have 
lain dormant or in potentia in reviews of modest scope. Physico- 
chemical embryology has, indeed, arrived at the stage immediately 
priox to birth, and all it needs is a skilful obstetrician, for, when once 
it has reached the light of day and has passed for ever out of the 
foetal stage, it will be well able to take care of itself. This obstetrical 
task is that which I have chosen and obviously enough it divides 
into three principal heads: first, to collect together out of all the 
original papers on the subject the facts which are known about the 
physico-chemical basis of embryonic development; second, to relate 
these facts to each other and to the facts derived from the labours 
of investigators in morphological embryology and " Entwicklungs- 
mechanik," and, third, to ascertain whether, from what is at present 
known, any generally valid principles emerge. 

I may as well say at the outset that in order to do this certain 
arbitrary boundary-lines are inevitable. The following arrangement 
has been adopted. Chronologically speaking, the prelude to all em- 
bryonic development is the maturation of the egg-cell, but this is not 
strictly embryology, and so has been relegated to an appendix. The 
egg-cell as a physico-chemical system is dealt with at the opening 
of Part III, and thereafter the physico-chemical aspects of develop- 
ment follow in order. No mention will be made of fertilisation, for 
this has been treated exhaustively by other writers (Lillie, Dalcq) 
and, after all, embryology presupposes fertiUsation whether natural 
or artificial. Nor in later chapters will any complete treatment be 


given of the events going on in the maternal organism during preg- 
nancy : for the present purpose the discussion will go as far into the 
mother as the placenta but no farther. Again, hatching or birth will 
put an end to the discourse as to the foetal state itself, save that, in 
the cases of animals which hatch before the yolk-sac is absorbed, 
their embryonic life is assumed to end when they first take food for 
themselves. Appendices are added dealing with the plant embryo 
and the insect pupa, which, in the later stages of metamorphosis, 
have points both of resemblance to and of difference from the growth 
of the embryo. It is natural to hope that the outcome of all this labour 
may be an increase of interest among biologists in this section of their 
domain, and a great accession to the number of those investigators 
who devote their energies to actual experiments in this new field. 

For it must be confessed that it is a new field. It has been opened 
up in very gradual stages: fitful and sporadic experiments on the 
constitution of embryonic tissues in the seventeenth century, a gradual 
growth of knowledge about the chemical composition of eggs in the 
eighteenth, a big increase of activity in the early nineteenth; d'lTxiug 
which appear the first observations on the physico-chemical changes 
taking place in the embryo during its development, and then in our 
own time a mass of very widely scattered work bringing the subject 
up to the "obstetrical" stage. Such a work as this, in my opinion, 
should not be compared with laboratory experiments in a derogatory 
sense, for, while it is true that facts are the ultimate court of appeal 
in any scientific discussion, yet at the same time the number of in- 
vestigators has grown to such extraordinary proportions in this century 
that some danger exists lest we should be so busily engaged in accu- 
mulating new facts as to be left with no time at all to devote any 
thought to those we have already. Classification, indexing, and 
maturer consideration about the facts we actually possess are at least 
as great a need at the present moment as the invention of new facts. 
"Everyone must realise", says Eugenio Rignano, "how much this 
theoretical elaboration, performed by means of analyses and com- 
parisons, of generalisations and hypotheses controlled and verified by 
the correspondence of facts with the results of the reasoning, is useful 
and necessary if one wishes to reach a progressive systematisation and 
an ever more synthetic vision of the confused mass of facts which 
experimentalists pour daily in a continuous stream into the scientific 


My predecessors in this work have been few in number. The volumes 
of Haller's, Buffon's, and Milne-Edwards' great treatises, in which 
they deal with the phenomena of generation, contain as much in- 
formation as was available up to 1863, but this is purely of historical 
interest to us. In 1885, W. Preyer, Professor of Physiology at Jena, 
published his Spezielle Physiologie des Embryo, which still remains a most 
valuable review, and indeed, even to-day, is the only existing book 
specially devoted to embryonic physiology. The present century 
has produced only three books which even touch upon my subject, 
namely, T. B. Robertson's Chemical Basis of Growth and Senescence, 
F. H. A. Marshall's Physiology of Reproduction and E. Faure-Fremiet's 
La Cinetique du Developpement. The first of these was admittedly written 
to support a particular theory, and in any case says comparatively 
little about physico-chemical embryology. The second and the third 
deal with it only as a constituent part of a much wider field. In 
Marshall's case, the whole array of facts relating to oestrus and 
breeding, fertilisation and fertility, lactation and sex determination, 
have to be dealt with, and only three chapters out of sixteen are 
devoted to the subject of this book. The first of these is contributed 
by W. Cramer, and covers the biochemistry of the sexual organs, in- 
cluding the unfertiUsed egg ; the second, which deals with foetal 
nutrition and the placenta, is by J. Lochhead ; and the third, by these 
two investigators together, is concerned with changes in the maternal 
organism during pregnancy. Admirable as these chapters are, they 
are now rather out of date. Moreover, though one or two corners 
of the field I have before me were covered in Marshall's book, it was 
from a quite different standpoint. 

Faure-Fremiet's work is exactly analogous; it deals with physico- 
chemical embryology only, as it were, in passing. The relevant dis- 
cussion takes up only two chapters out of seven ; the rest are occupied 
with tissue culture, growth of protozoal populations, and general 
cytology. His book covers, it might be said, the third and fourth 
corners : all the main expanse of the field remains. 

Thus neither of these books deals with physico-chemical embryo- 
logy in an exhaustive and comprehensive fashion, treating it as, in 
my view, it ought to be treated, with the thoroughness which is 
deserved by a new branch of natural knowledge. Inseparable, how- 
ever, from thoroughness of treatment is the submergence of the parts 
of more general interest under a mass of detail, and it may be well. 


therefore, to mention now what sections of the book could be said 
to be most valuable to any student of general biology. Part i comes 
in this class, and of Part iii, the middle portion of Section i, all of 
Sections 2, 3, and 5, thelatter half of Section 7, Sections 8, 9 (especially 
the end), 11, possibly 18, and finally the Epilegomena. 

For my models in the preparation of this book, if it is permissible 
to name them, I have taken, Growth and Form by d'Arcy Thompson, 
surely the most scholarly work produced by a biologist in our time, 
and The Physiology of Reproduction by F. H. A. Marshall, already 
mentioned, which showed to all successors, in my opinion, how a 
colossal array of facts can be welded together into an absorbing and 
readable book, I am conscious that I shall not attain the level of 
these classics of modern biology, but then 

.... Pauci, quos aequus amavit 
Jupiter, aut ardens evexit ad aethera virtus. 

The progress of any branch of natural knowledge can be best 
described as a continual pilgrimage towards the quantitative. QuaUties 
can never be altogether left out of account and this is what makes 
it impossible for science to achieve its end with absolute finality. Yet 
an association with the probably unattainable is common to all the 
great types of man's activity. But "Fuyez toujours les a peu pres", 
as O. W. Holmes used to put it, is a proper maxim for the scientific 
mind, and whatever this book can do towards making embryology 
an exact science will be its final justification. 





. . . .to measure all things that can be measured, and to 
make measurable what cannot yet be measured. 


THE THEORY OF ^^^-^S^aj^, 


Philosophy, Embryology, and Chemistry 

The penetration of physico-chemical concepts into embryology 
has not been entirely peaceful. "In experimental embryology", it 
has been said, "concepts borrowed from the physical sciences do not 
admit of calculations being made, and until they do they are not 
really playing the same role as they do in the sciences from which 
they have been borrowed and for which they were devised." "Nothing 
is more clear", says another writer, "in chemistry and physics than 
that identical results follow upon identical causes. Introduce a dis- 
turbing element, even a small one, into your experiment, and the 
experiment will fail. Such is not the case with the developing egg." 
W. McDougall, too, endows the egg with good intentions. "The 
embryo", he says, "seems to be resolved to acquire a certain form 
and structure, and to be capable of overcoming very great obstacles 
placed in its path. The development of the forms of organisms seems 
to be utterly refractory to explanation by mechanical or physico- 
chemical principles." Finally, J. A. Thomson goes farther than them 
all, and does not hesitate to say, "It is a mere impious opinion that 
development will one day be described in terms of mechanics". 
Chapter iv of his Gifford Lectures illustrates the antagonistic attitude 
to physico-chemical embryology in its most acute form. 

It can hardly be a coincidence that so many among the great 
embryologists of the past were men of strongly philosophic minds. 
It would be absurd to support this opinion by citing Aristotle, but 
it holds less obviously true of William Harvey, whose book on genera- 
tion is full of thoughts about causation, and in the cases of Ernst 
von Baer, Ernst Haeckel, Wilhelm Roux, Hans Driesch, dArcy 
Thompson and J. W. Jenkinson, there is no doubt about it. It is not 
really surprising, for of all the strange things in biology surely the 
most striking of all is the transmutation inside the developing egg, 
when in three weeks the white and the yolk give place to che animal 
with its tissues and organs, its batteries of enzymes and its dehcately 
regulated endocrine system. This coming-to-be can hardly have failed 


to lead, in the minds of those most intimately acquainted with it, to 
thoughts of a metaphysical character. Nor, it seemed, did those who 
worked on it do much to diminish its wonder. "Neither the schools 
of physicians", as Harvey said, "nor Aristotle's discerning brain, 
have disclosed the manner how the Cock and its seed, doth mint and 
coine, the chicken out of the Ggg,'^ Or, in the words of Erycius 
Puteanus, "I will neglect gold, and will praise what is more precious 
than any metal, I will despise feasts, and will set forth praises of 
something better than any food or drink. If you would know of what 
it is that I intend to speak, it is the egg; men marvel at the sun, at 
meteors flung from heaven, at stars swimming therein, but this is 
the greatest of all wonders". Here, however, there is one significant 
thing. It is that the very chapter of Harvey's book in which the 
preceding remark is found has as its heading "The Efficient Cause 
of the Chicken, is hard to be found out". It certainly was, but the 
right clue was in the heading to that exercitation. 

This close association of embryology with philosophy, then, made 
it necessary to discuss at the outset of this book certain points in the 
more theoretical regions of biology, and, as it were, to defend from 
a theoretical angle the extension of the domain of physics and 
chemistry over embryology. I might have entitled this part of the 
book "The philosophy of embryology", but, in deference to those 
metaphysicians who rightly insist that the word philosophy should 
only be used of a definite system of experience which looks at the 
universe as a corporate whole, I adopted the present heading. Under 
it I propose to discuss the exact status of the chemical aspect of 
embryology. For many biologists, having perhaps insufficiently con- 
sidered the nature of the scientific method, think it likely that 
the discoveries of modern times may allow of some other basis for 
biology than mathematical physics and that the scientific niethod 
may rightly be different in biology from what it is in chemistry. It 
is this factor in our present intellectual climate which makes it neces- 
sary to preface by a philosophical discussion a book in which the 
concepts of physics and chemistry are extended to a field of biology 
where they have never before received more than a conventional and 
formal reverence. 

The aim of all studies in physico-chemical embryology must be 
that expressed by T. H. Huxley when he said, " Zoological Physiology 
is the doctrine of the functions or actions of animals. It regards 


animal bodies as machines impelled by certain forces and perform- 
ing an amount of work which can be measured and expressed 
in terms of the ordinary forces of nature. The final object of 
physiology is to deduce the facts of morphology on the one hand 
and those of oecology on the other hand from the laws of the mole- 
cular forces of matter". It may be regarded as very noteworthy 
that Huxley here puts morphology as secondary to physiology and 
as it were derivable from it; he does not place morphology and 
physiology on two high places, "neither afore or after other", as 
has so often been done, but he plainly states his view that the 
anatomical aspect of animals, their external and internal forms, could 
be deduced from the interplay of physico-chemical forces within 
them, if we only knew enough about those forces. This is the idea 
of the primacy of function. It seems always to have two meanings, 
firstly, the Epicurean-Lucretian one which Huxley adopts here and 
Roux so brilliantly developed, in which shape is regarded as the 
outward and visible sign of the properties of matter itself, and, 
secondly, the Aristotelian one emphasised by J. B. de Lamarck's 
writings in the eighteenth century, and in our time by E. S. Russell's 
great work Form and Function, in which psychical factors are intro- 
duced as the essential elements in the ultimate analysis of shape. In 
both these interpretations, function has the priority over form, but 
the meaning of function is the point of difference. Some biologists, 
however, seem to think that physiology and morphology are cate- 
gorical, and the latter is emphatically not reducible to or derivable 
from the former. The two spheres of study represent, for them, 
correlative and immiscible disciplines, morphology aiming ultimately 
at solid geometry, physiology at causation, and "rerum cognoscere 
causas" is not the basic desire of the scientific mind. They object 
to the view which regards "the ovum as a kind of chemical device 
wound up and ready to go off on receipt of a stimulus, the task of 
the causal morphologist being to disentangle the complex of events 
which constitute the unwinding process" (Woodger), complaining 
that in this view no account is taken of the past history of the 
race, which is left to genetics, again a causal discipHne. To some 
extent these opinions spring from a conviction that the analytical 
method is inapplicable to a living being because it is an organism, and 
of that there is more to be said. But they also arise from a profound 
unwillingness to subsume biology under physics and a desire to uphold 

10 THE THEORY OF [pt. 

"the autonomy of biology". This precludes the promise of an ever- 
increasing homogeneity in the structure of science, and hence an 
ever-increasing simplicity. 

The Historical Perspective 

That the older embryologists awaited the extension of physico- 
chemical conceptions to embryology is no mere matter of conjecture. 
Until the mechanical theory of the universe had been consolidated 
by the " corpuscularian philosophy" of the seventeenth century it 
would be useless to look for illustration of this, but by 1674 John 
Mayow was tracing the part played by the " nitro-aerial particles" 
in the development of the embryo, and in 1732 Hermann Boerhaave 
was discussing chemical problems with explicit reference to embryonic 
development. Many other examples of this point of view in the 
eighteenth century will be given later. Then, when the second decade 
of the nineteenth century had nearly gone, von Baer, perhaps the 
greatest of all embryologists, was careful to preface his Entwicklungs- 
geschichte by a careful account of all that was known about the 
chemical constitution of the Qgg, and that, although his philosophical 
inclinations were deeply vitalistic, and even his practical interests 
morphological. In Roux, of course, this future reference came out 
explicitly, and the extension of biochemistry into embryology was 
allowed for and foreseen. An early instance was the association be- 
tween Wilhelm His and Hans Miescher. Miescher, writing to Hoppe- 
Seyler in 1872 said, "I am now collecting material from fishes, 
birds, and amphibia to lead to a chemical statics of development. 
With this end in view I shall do analyses of ash, nuclein, and lecithin". 

Embryology before Harvey, however, was rigidly Aristotelian, a 
statement the meaning of which George Santayana has lucidly ex- 
plained. "Aristotle", said he, "distinguished four principles in the 
understanding of Nature. The ignorant think that these are all, 
equally, forces producing change, and the cooperative sources of all 
natural things. Thus, if a chicken is hatched, they say that the Efficient 
Cause is the warmth of the brooding hen, yet this heat would not 
have hatched a chicken out of a stone, so that a second condition, 
which they call the Material Cause, must be invoked as well, namely, 
the nature of an egg; the essence of eggness being precisely a capacity 
to be hatched when warmed gently — because, as they wisely observe, 
boiling would drive away all potentiality of hatching. Yet, as they 


further remark, gentle heat-in-general joined with the essence-of- 
eggness would produce only hatching-as-such and not the hatching 
of a chicken, so that a third influence, which they call the Final 
Cause, or the End-in-view, must operate as well, and this guiding 
influence is the divine idea of a perfect cock or a perfect hen presiding 
over the incubation and causing the mere eggness in the egg to 
assume the likeness of the animals from which it came. Nor, finally, 
do they find that these three influences are sufficient to produce here 
and now this particular chicken, but are compelled to add a fourth, 
a Formal Cause, namely, a particular yolk, a particular shell, and 
a particular farmyard, on which and in which the other three causes 
may work, and laboriously hatch an individual chicken, probably 
lame and ridiculous despite so many sponsors." The Aristotelian 
account of causation could not be better expressed. Santayana puts 
this description of it into the mouth of Avicenna in his imaginary 
dialogue, and makes him go on to say, "Thus these learned babblers 
would put nature together out of words, and would regard the four 
principles of interpretation as forces mutually supplementary com- 
bining to produce material things ; as if perfection could be one of 
the sources of imperfection or as if the form which things happen 
to have could be one of the causes of their having it. Far differently 
do these four principles clarify the world when discretion conceives 
them as four rays shed by the light of an observing spirit". In this 
last observation we may perhaps trace the germ of the Copernican 
revolution in philosophy effected by Kant, if we may take it to enclose 
the idea of the activity of the experient subject in all perception. 

In science generally, however, the x\ristotelian conceptions went 
without serious contradiction, and thus formed the framework for all 
the embryological work that was done, as, for instance, by Albertus 
Magnus. Owing to its association with the idea of the plan of a 
divine being, the final cause tended in the Middle Ages to eclipse 
the others. In the seventeenth century this feeling is well shown in 
a remarkable passage, which occurs in the Religio Medici of Sir Thomas 
Browne: "There is but one first cause, and four second causes of all 
things; some are without Efficient, as God; others without Matter, as 
Angels; some without Form, as the first matter; but every Essence 
created or uncreated, hath its Final cause, and some positive End both 
of its Essence and Operation ; this is the cause I grope after in the 
works of Nature ; on this hangs the providence of God ; to raise so 

12 THE THEORY OF [pt. 

beauteous a structure as the World and the Creatures thereof, was 
but his Art; but their sundry and divided operations, with their 
predestinated ends, are from the Treasure of his Wisdom. In the 
causes, nature, and affections of the EcHpses of the Sun and Moon 
there is most excellent speculation, but to profound farther, and to 
contemplate a reason why his providence hath so disposed and 
ordered their motions in that vast circle as to conjoyn and obscure 
each other, is a sweeter piece of Reason and a diviner point of 
Philosophy; therefore sometimes, and in some things, there appears 
to me as much Divinity in Galen his books De Usu Partium, as in 
Suarez' Metaphysicks: Had Aristotle been as curious in the enquiry 
of this cause as he was of the other, he had not left behind him an 
imperfect piece of Philosophy but an absolute tract of Divinity". 
This was written in Harvey's time, and in Harvey's thought the four 
causes were still supreme ; his De Generatione Animalium is deeply con- 
cerned with the unravelling of the causes which must collaborate in 
producing the finished embryo. But the end of their domination was 
at hand, and the exsuccous Lord Chancellor, whose writings Harvey 
thought so little of, was making an attack on one of Aristotle's causes 
which was destined to be peculiarly successful. There is no need to 
quote his immortal passages about the "impertinence", or ir- 
relevance, of final causes in science, for they cannot but be familiar 
to all scientific men. Bacon demonstrated that from a scientific point 
of view the final cause was a useless conception; recourse to it as an 
explanation of any phenomenon might be of value in metaphysics, 
but was pernicious in science, since it closed the way at once for 
further experiments. To say that embryonic development took the 
course it did because the process was drawn on by a pulling force, 
by the idea of the perfect adult animal, might be an explanation of 
interest to the metaphysician, but as it could lead to no fresh experi- 
ments, it was nothing but a nuisance to the man of science. Later 
on, it became clear also that the final cause was irrelevant in science 
owing to its inexpressibility in terms of measurable entities. From 
these blows the final cause never recovered. In England the seven- 
teenth century was the time of transition in these aflfairs, and in such 
books as Josfeph Glanville's Plus Ultra and Scepsis Scientifica, for in- 
stance, and Thomas Sprat's Defence of the Royal Society, the stormy 
conflict between the "new or experimental philosophy" and the 
Aristotelian "school-philosophy" can be easily followed. Francis 


Gotch has given a delightful account of the evening of AristoteUanism, 
but it involved a stormy sunset, and the older ideas did not give 
way without a struggle. Harvey's work is perfectly representative of 
the period of transition, for, in his preface under the heading "Of the 
Method to be observed in the knowledge of Generation", he says, 
"Every inquisition is to be derived from its Causes, and chiefly from 
the Material and Efficient". As for the formal cause. Bacon expressly 
excluded it from Physic, and it quietly disappeared as men saw that 
scientific laws depended on the repeatableness of phenomena, and 
that anything unique or individual stood outside the scope of science. 
Thus in the case of the developing egg, the formal (the particular 
farmyard, etc.) and the final causes are scientifically meaningless, 
and if it were desired to express modern scientific explanation in 
Aristotelian terminology, the material and efficient causes would 
alone be spoken of, essence-of-eggness being a "chymical matter" 
as well as the heat of the brooding hen. 

Obstacles to Chemical Embryology 

The complexity of living systems, however, is such that many 
minds find it difficult to accept this physico-chemical account as the 
most truly scientific way of looking at it. This is doubtless due in part 
to an erroneous notion, which is yet very tenacious of existence, that 
the mechanical theory of the universe must, if accepted at all, be 
accepted as an ultimate ontological doctrine, and so involve its sup- 
porter in one of the classical varieties of metaphysical materialism. 
It cannot be too strongly asserted that this is not the case. To imagine 
that it is, is to take no account of the great space that separates us 
from the last century. "When the first mathematical, logical, and 
natural uniformities", said WilHam James, "the first Laws, were 
discovered, men were so carried away by the clearness, beauty, and 
simplification that resulted that they believed themselves to have 
deciphered authentically the eternal thoughts of the Almighty. His 
mind also thundered and reverberated in syllogisms. He also thought 
in conic sections, squares, and roots and ratios, and geometrised like 
Euclid. He made Kepler's laws for the planets to follow, he made 
velocity increase proportionately to the time in falhng bodies; he 
made the laws of the sines for light to obey when refracted; he 
established the classes, orders, families, and genera of plants and 
animals, and fixed the distances between them." 

14 THE THEORY OF [pt. 

Far different is the account of itself which science has since learned 
to give. But this change of attitude is not a revolt against thought 
as such, or against reason as such ; it is only a loss of belief in the 
literal inspiration of the formulae proper to science. It would be just 
as extravagant to claim that the scientific investigator of the twentieth 
century sets down absolute truths in his laboratory notebook, and, 
armed with an infallible method, explores the real structure of an 
objective world, as it would be fantastic to claim that Jehovah 
dictated an absolute code of the good to Moses on Mount Sinai. To 
say that the development of a living being can best be described in a 
metrical or mechanical way is not to say that it is metrical or me- 
chanical and nothing else. The physico-chemical embryologist is not 
committed to any opinion on what his material really is, but he is 
committed to the opinion that the scientific method is one way of 
describing it, and that it is best to apply that method in its full rigour 
if it is to be applied at all. In other words, following the train of 
thought of William James, he does not assert that the courts of Heaven 
as well as those of our laboratories resound with expressions such as 
"organisers of the second grade," and "so many milHgrams per cent." 
The mechanical theory of the world, which is, as many beHeve, 
bound up indissolubly with one of the ultimate types of human 
experience, can no longer be considered as necessarily involving the 
exclusion of other theories of the world. Or, put in another way, it 
is a theory of the world, and not a pocket edition of the world itself 

But before bringing forward any arguments in support of this 
attitude and in defence of physico-chemical embryology, it will be 
well to consider briefly those theoretical tendencies in modern biology 
which go together under the inexact adjective "neo-vitalistic", for 
their influence in scientific thought has been far-reaching. To deal 
critically with them is not a waste of time, for, were we to adopt 
any one of them, we should find that the notion of embryology as 
complicated biophysics and biochemistry would have to be abandoned, 
and quite other means of approach (never, indeed, very well defined) 
would have to be used. 

The Stumbling-block of Hormism 

Hormism, or "Psychobiology," may be dealt with in a few 
words. Chiefly supported by A. Wagner in Germany, and by 
E. S. Russell and L. T. Hobhouse in this country, it holds that — to 


use Lloyd Morgan's terminology — a physiological tale cannot be told 
separately from a psychological tale. Instead of expressing living 
processes in terms of physical causes and effects, the hormists wish 
to regard unconscious striving as the essential urge in life, and such 
conceptions as food, rest, fatigue, etc., as irreducible biological cate- 
gories. These thinkers do not often acknowledge their debt to Galen 
of Pergamos, who put forward, as early as a.d. 170, an essentially 
similar conception as the basis of his biology. In the treatise On the 
Natural Faculties he says, "The cause of an activity I term a faculty.... 
Thus we say that there exists in the veins a blood-making faculty, 
as also a digestive faculty in the stomach, a pulsatile faculty in the 
heart, and in each of the other parts a special faculty corresponding 
to the function or activity of that part". He also said, "We call it 
a faculty so long as we are ignorant of the cause which is operating", 
but he never actually suggested any such underlying cause, and 
seems to have thought it impossible to ascertain. So do the hormists. 
According to them the actions of protozoa are to be described in 
terms of avoiding responses, seeking responses and the like, language 
which, as they claim, is much simpler than the complex terminology 
of surface tension and molecular orientation. Everything, of course, 
depends on what is meant by simple. To say that a protozoon seeks 
the light is evidently more naive than to say that a dimolecular 
photochemical reaction takes place in its protoplasm leading to an 
increase of lactic acid or what not on the stimulated side, but since 
the latter explanation fits into the body of scientific fact known 
already it is open to the biochemist to say that, for his part, he. con- 
siders the latter explanation the simpler. It is, in fact, simpler in 
the long run. Psychobiology or hormism differs from the other 
forms of neo-vitalism because it insists on retaining " commonsense " 
explanations in biology as categories of biological thought beneath 
which it is impossible to go. It dismisses the entelechy of dynamic 
Teleology, on the ground that it acts, as it were, in addition to the 
mechanistic schema, accepting the latter fully but interfering in it. 
It resembles much more finaUsm and organicism, but lays stress 
rather on the unconscious striving force which seems to animate 
colloidal solutions of carbohydrates, fats, and proteins. It resembles 
the Behaviourism of J. B. Watson superficially by emphasising animal 
behaviour, but it fundamentally differs, for it asks the question — Does 
an animal see the green light and the red light in this experiment 

i6 THE THEORY OF [pt. 

as we do, or does it see them as two shades of grey as colour-blind 
people do? while the behaviourist asks — Does it respond according 
to difference of light-intensity or difference of wave-lengths ? Hormism, 
in fact, recurs continually to psychical factors. Samuel Butler, for 
instance, one of its principal exponents, wrote, "I want to connect 
the actual manufacture of the things a chicken makes inside an egg 
with the desire and memory of the chicken so as to show that one 
and the same set of vibrations at once change the universal sub- 
stratum into the particular phase of it required" (cf. ^ rov hwdixei, 
6vTo<i ivreXex^ta fj tolovtov) "and awaken a consciousness of and a 
memory of and a desire towards this particular phase on the part of 
the molecules which are being vibrated into it". "The Hormist 
contends", says Lloyd Morgan, "that something which is very 
difficult to distinguish from a ' plan-in-mind ' on the part of the 
embryo chick or rabbit does freely determine the course of events 
in specific growth from egg to adult. This, I urge, is a metaphysical 
hypothesis which goes beyond biology or psychology as branches of 

Finalism as a Rock of Offence 

Finalism and dynamic Teleology are closely connected, for both 
of them embody an attempt to go back to the Aristotelian inclusion of 
the final cause as an integral essential of scientific explanation, and 
to regard the Baconian attitude to teleology as a mistake. They solve 
Kant's antinomy of the teleological judgment simply by deleting the 
proposition, and leaving the counter-proposition. They are weakest 
on their practical side, for their supporters do not suggest any altera- 
tions which might be made in scientific method, although their 
fundamental assumptions plainly require it. The principal repre- 
sentative of finalism is Eugenio Rignano, and dynamic teleology 
has been for the most part upheld by Hans Driesch. 

Rignano, in his Qii' est-ce-que la Vie? and his Biological Memory has 
contended that, though the mechanical concept of the universe may 
be perfectly satisfactory as a description of the world of physics, yet 
animals and plants show so much purposiveness that mechanical 
categories are absolutely inadequate for them. Biology, therefore, 
cannot be complicated physics and chemistry, but must be something 
sui generis and with its own methods and laws. "The long debate 
between vitalists and mechanists," he says, "in attempting to give 


an explanation of life, cannot lead to any conclusion unless that 
fundamental characteristic common to all vital phenomena of pre- 
senting a purposive, teleological, or finaUstic aspect in their most 
typical manifestations is first thoroughly examined." The most suc- 
cinct account of his views and of the exact biologist's answer to them will 
be found in his Man Not a Machine, and in the volume Man a Machine 
in the same series. The way in which they affect embryology is 
significant, and may be found in his chapter called "Finalism of the 
generative and regenerative phenomena". "Even if", he says, "the 
organism could be explained as a physico-chemical machine, there 
would still remain to be explained the most fundamental thing — how 
the machine constructed itself The purposiveness of the ontogenetic 
development is too evident to be denied. It results from the con- 
vergence of manifold morphogenetic activities to one sole end, that 
is, to the formation of a marvellous functional unity, every part of 
which serves to maintain the life and guarantee the well-being of the 
whole. The embryo in its development manifests at every stage a 
' harmony of composition ' as Driesch calls it, which has a touch of 
the marvellous ; parts and elements of an organ develop independently, 
but when they have finished their development they are found to 
fit together perfectly like the parts of a machine and the one so 
answers to the other that they unitedly form one complex organ. 
Thus the mouth and intestine of the sea-urchin begin their develop- 
ment at two points distant from each other and develop indepen- 
dently, but as they grow the one moves towards the other, so that 
when development is ended they fit together perfectly and form a 
single canal." This passage illustrates the line of argument found 
throughout Rignano, and I will not remark on it further than to 
draw attention to the mention of the marvellous in it, another hint, 
if any were needed, of that strain of misplaced "numinous instinct" 
which seems to be present in all biological vitaHsts. Omnia exeunt 
in mysterium would seem to be "a discouraging maxim" for the 
scientific worker. "The direction", Rignano goes on to say, "of 
ontogenetic development toward a predetermined end is also in- 
fluenced by the fact that the embryo overcomes early disturbances 
which might deflect it from its course. Ontogenesis thus seems to be 
marshalled by some occult intelligence or entelechy in the same way 
that the construction of a machine and the direction of its work is 
presided over by the mind of the engineer." 

i8 THE THEORY OF [pt. 

Rignano's arguments are open to grave objection on two main 
grounds, first, that he regards biology as suffering more than physics 
from the teleology of things, and, second, that he wishes to bring the 
concept of purposiveness back into natural science. 

The first of these is inadmissible both on philosophic and scientific 
grounds. Bernard Bosanquet best expresses the former attitude. He 
was led to his conclusions by the conviction that James Ward and 
other opponents of scientific naturalism had gone too far in their 
polemics against the mechanical theory of the universe, and had 
rested the case for teleology only "on the capacity of the finite 
consciousness for guidance and selection". This he considered a 
mistake. "Things are not teleological", he said, "because they are 
de facto purposed but necessary to be purposed because they are 
teleological.,.. The foundations of teleology in the universe are far 
too deeply laid to be accounted for by, still less restricted to, the 
intervention of finite consciousness. Everything goes to show that 
such consciousness should not be regarded as the source of teleology 
but as itself a manifestation falling within wider manifestations of 
the immanent individuality of the real." Bosanquet proceeds, fol- 
lowing out the thought of his teacher, Lotze, "The contrast, then, 
of mechanism with teleology, is not to be treated as if elucidated 
at one blow by the antithesis of purposive consciousness and the 
reactions of part on part. It is rooted in the very nature of totality, 
which is regarded from two complementary points of view, as an 
individual whole, and as constituted of interacting members". But 
Rignano's arguments are unsatisfactory also from a scientific angle, 
and here the objection comes from Lawrence J. Henderson, whose 
book The Fitness of the Environment, probably the most important 
contribution to biological thought in this century, is never referred to 
by Rignano. It cannot now be necessary to recount how Henderson 
examined the question of the finality of our present scientific know- 
ledge, and, judging that it was considerable, went on to enquire into 
the properties of the elements and compounds principally associated 
with life. His conclusion was that living animals and plants exist in 
an environment just as fitted for them as they are for it, that the 
Darwinian concept of fitness works, indeed, both ways, and that 
there is a reciprocity between organism and environment so that 
every teleological action done by an individual organism bears upon 
it the image and superscription of universal teleology. Thus the 


conclusion of the thought of Bosanquet and Henderson was that, 
though teleology was a conception which it was impossible to 
do without, yet any limitation of it to, or special association of it 
with, living organisms, was inadmissible. The question remained, 
What has teleology to do with science? 

This point has been approached best by J. W. Jenkinson with his 
usual clarity. "Those who uphold teleological doctrine", he said, 
"seem to have fallen into a confusion between two different things, 
the formal and the final cause. The material, efficient, and formal 
causes, if we mean by the last the idea of the effect in the mind of a 
sentient being, all precede in time the occurrence of the effect; and 
this kind of teleology is not, as it is asserted to be, a doctrine of final, 
but one of formal causes. The final cause stands for the use to which 
an object is to be put, the effect it will produce, the function it will 
perform, which obviously succeed in time the existence of the object 
itself The final cause, then, cannot be taken as ever determining in 
time the existence of the object itself, and is therefore a conception 
which belongs not to science but to metaphysics. The only necessary 
conditions of a phenomenon ascertainable by science are those 
material and efficient causes which precede it." Or, as Streeter puts 
it, "If there is purpose in nature, we ought not to expect science to 
reveal it. Purpose is activity, the direction of which is determined 
by an end, that is, by an apprehension of quality or value. But 
quaUty cannot be measured, and therefore from its essential nature 
it — and along with it purpose — lies outside the sphere of science". 
Or, finally, to go straight to the fountain-head, "If I say", says 
Kant, "that I must judge according to merely mechanical laws of 
the possibility of all events in material nature and consequently of all 
forms regarded as its products, I do not therefore say: they are 
possible in this way alone. All that is impUed is: I must always 
reflect on them according to the principle of the mere mechanism 
of nature and consequently investigate this as far as I can ; because 
unless this Ues at the basis of investigation there can be no proper 
knowledge of nature at all". Purposiveness, in fact, is not a concep- 
tion which interlocks with quantitative treatment; that mathematical 
expression of relationships which is the ideal type of all science 
has here nothing upon which to impinge, and the pulling force, 
perpetually going on before, eludes and must always elude, if this 
analysis is correct, the advancing web of mechanical explanation. 

20 THE THEORY OF [pt. 

If, then, Bacon and his successors were right in banishing the 
concept of teleology from scientific thought, the physico-chemical 
embryologist need not be alarmed by the finalism with which, 
according to Rignano, the whole of ontogenetic development is suf- 
fused. In fact, it is not the phenomenon, but only one way of looking 
at it, that is finalistic, and it is this aspect of it that must be neglected 
in scientific work if the gravest confusion is to be avoided. Is there 
need for the biologist to be any more afraid of the Drieschian en- 
telechy (Aristotle's eVreXe^em Actuality) making what might be into 
what is and directing from within the development of the embryo in 
the egg or the uterus? The word "entelechy" as used by Aristotle 
meant that which exists in the highest sense of the word, whether 
actually or potentially, e.g. the sword in the mind of the swordmaker 
before a single one of the necessary operations of manufacture had 
been begun. The entelechy therefore operated on the process in 
question by means of the final cause, and did not reside in the 
changing entity if it was dead like the sword, though it did if it was 
alive like the embryo. Driesch frequently says that he uses the word 
in a quite different sense from Aristotle, but the majority of his 
readers find it impossible to discover any essential point of divergence. 
He does at any rate make it much more precise than Aristotle, for he 
defines it as a non-spatial element in the living being, which at one 
time suspends possible action and at another time relaxes such 
suspension, acting in this way as the bearer of "individualising 
causality" and bringing the animal from potentiality into actuality. 

It seems that this inherent immanent formative power has been 
translated by biologists of every period since Aristotle into the lan- 
guage of their time. Just as Driesch now tries to acclimatise it to the 
unfavourable environment of a post-Cartesian world, so St Gregory of 
Nyssa, who lived about a.d. 370, clothed it in patristic terminology, 
and produced a theological variety of neo-vitalism. His most im- 
portant biological works, the irepl KaraaKevrjq dvdpcoirov, On the making 
of Man, and Trepl '^v^V'^i On the Soul, contained such passages as these, 
"The thing so implanted by the male in the female is fashioned 
into the different varieties of limbs and interior organs, not by the 
importation of any other power from without, but by the power 
which resides in it transforming it". And elsewhere, "For just as a 
man when perfectly developed has a soul of a specific nature, so at 
the fount and origin of his life, he shows in himself that conformation 


of soul which is suitable for his need in its preparing for itself its 
peculiarly fit dwelling-place by means of the matter implanted in 
the maternal body, for we do not suppose it possible that the soul is 
adapted to a strange building, just as it is not possible that a certain 
seal should agree with a different impression made in wax". 

Thus the soul makes its body as if it were a gem making a stamp 
upon some soft substance, and acting during embryogeny from 
within — a conception essentially like that of Driesch. We shall see 
later how many Renaissance authors adopted similar views, e.g. 
Fienus. "No unsouled thing", says Gregory, "has the power to 
move and to grow. Yet there is no doubt that the embryo moves 
and waxes big as it is fed in the body of the mother." There is nothing 
new about dynamic teleology; it is by no means the outcome of 
newly ascertained facts : it recurs from time to time in the history of 
biological thought because it is the natural result of an unscientific 

I do not propose to discuss here the facts which originally led 
Driesch to the views expressed in his Science and Philosophy of the 
Organism, for they are very well known, and have been shown by 
J. W. Jenkinson, H. S. Jennings, H. C. Warren and A. E. Boveri, 
among others, to be interpretable on quite other lines. Nor shall I 
demonstrate by a comparison of passages from Driesch and Paracelsus 
how closely the conception of immanent formative force or entelechy 
approaches the master-archaeus of Paracelsus and the later iatro- 
chemists such as Stahl, for Driesch has done it himself in his History 
and Theory of Vitalism. The inference from it is that the Drieschian 
entelechy has been and will be of no more use as a practical working 
hypothesis for the laboratory than the archaeus was in the past. 

Driesch's dynamic teleology is open to more serious and funda- 
mental objections. These were not obvious at the first appearance 
of his Gifford Lectures, but were clearly brought to light through 
the controversy which Jacques Loeb had with H. S. Jennings and 
which resulted in the publication of their respective books, Forced 
Movements, Tropisms, and Animal Conduct and The Behaviour of the Lower 
Organisms. Loeb's theory of tropisms entirely dispensed with any 
psychological factors, but Jennings upheld the view that they might 
be legitimately brought under scientific discussion, provided they 
were regarded as being determined as well as determining. This led 
him to make a new enquiry into scientific methodology, and he 

22 THE THEORY OF [pt. 

published his results in a valuable series of papers from 1911 to 191 8. 
He concluded that the pursuance of laboratory work demands as its 
minimum of system what he called "Radical Experimental Deter- 
minism", and that there was difference of opinion as to whether 
this might regard conscious or unconscious mental processes as links 
in the chain of determinate causation. On this point Jennings and 
Loeb were antagonists, but both were united against Driesch, from 
whose writings it now appeared that psychical events might or might 
not affect physical events according to circumstances, and that the 
entelechy was subject to no general laws. Neal had maintained that 
the experimentally discoverable perceptual determiners in living 
things were insufficient to account for the effects produced in them. 
Jennings pointed out that, if this meant that the non-perceptual 
(mental) determiners acted supplementarily to the others and not 
instead of them, it was compatible with radical experimental deter- 
minism. But, if it was said that some of the determiners were non- 
perceptual and could not be known at all, then it was incompatible. 
Now it was just this that Driesch had been saying. "A complete 
knowledge", he wrote, "of all physico-chemical things and relations 
(including possible relations) of a given system at a time t would 
not give a complete characterisation of that system if it is a living 
system. . . . Practically we may say that complete knowledge of the 
physico-chemical constitution of a given egg in a given state and of 
the behaviour following this constitution in one case, implies the 
same knowledge for other cases (in the same species) with great 
probability. But this is a probability in principle and can never be 
more. It would not even be a probability if we did not know the 
origin of a given egg in a given state, i.e. that the egg was the tgg, 
say, of an ascidian. But to know this history or origin, is of course, 
already more than simply to know its physico-chemical constitution 
and its consequences in one case, which suffices in the realm of the 
inorganic. It may be that the eggs of echinoidea, fishes, and birds, 
are the same in all the essentials of physico-chemical constitution. 
Something very different happens in each case on account of the 
different entelechies. In spite of this we know with great probability 
what will happen from one case if we know that this egg comes 
from a bird and that from an echinoid. Therefore, practically, ex- 
perimental indeterminism is not a great danger for science." 

But the matter was taken up by various writers, and Lovejoy, 


especially, defended Driesch from the charge of interfering with the 
fundamental necessities of scientific thought. Jennings, however, 
was able to publish in reply letters from Driesch in which these 
implications of his position were fully admitted. "Two systems abso- 
lutely identical in every physico-chemical respect may behave differ- 
ently under absolutely identical conditions if the systems are living 
systems. For the specificity of a certain entelechy is among the 
complete characteristics of a living organism and about this entelechy 
knowledge of physico-chemical things and relations teaches abso- 
lutely nothing." Such a basis for experimental work was generally 
felt to carry with it its own condemnation. 

It is interesting to recall, in this connection, the vivid account 

given by Claude Bernard of the polemic he had with Gerdy at 

the Philomathic Society in Paris, for the Driesch-Lovejoy-Jennings 

controversy simply repeated on a larger scale the arguments 

of the two Parisian biologists sixty years before. "In 1859," 

says Claude Bernard, "I made a report to the Philomathic 

Society in which I discussed the experiments of Brodie and 

Magendie on ligature of the bile-duct, and I showed that the divergent 

results which the two experimentalists reached depended on the fact 

that one operated only on dogs and tied only the bile-duct, while 

the other operated only on cats, and, without suspecting it, included 

in his ligature both the bile-duct and a pancreatic duct. Thus I 

explained the difference in the results they reached and concluded 

that in physiology as everywhere else experiments are rigorous and 

give identical results wherever we operate in exactly similar Conditions. 

A propos of this a member of the Society took the floor to attack my 

conclusions ; it was Gerdy, a surgeon at the Charite, professor in the 

faculty of medicine and known through various works in surgery 

and physiology. 'Your anatomical explanation of these experiments', 

said he, 'is correct, but I cannot accept your general conclusions. 

You say, in fact, that the results of experiments in physiology are 

identical; I deny it. Your conclusion would be correct for inert 

nature but cannot be true for living nature. Whenever life enters 

into phenomena', he went on, 'conditions may be as similar as we 

please, the results may still be different.' To support his opinion Gerdy 

cited cases of individuals with the same disease, to whom he had 

given the same drugs with different results. He also recalled cases 

of like operations for the same disease, but followed by cure in one 

24 THE THEORY OF [pt. 

case and death in another. These differences, according to him, all 
depended on life itself altering the results, though the experimental 
conditions were the same, but this could not happen, he thought, 
in the phenomena of inert bodies, where life does not enter. Opposi- 
tion to these ideas was prompt and general in the Philomathic 
Society. Everyone pointed out to Gerdy that his opinions were 
nothing less than a denial of biological science, but he would not 
give up his ideas and entrenched himself behind the word 'vitality'. 
He could not be made to understand that it was only a word, devoid 
of meaning and corresponding to nothing, and that saying that some- 
thing was due to vitality amounted to calling it unknown." The 
only difference between Driesch and Gerdy seems to be that Driesch's 
arguments rested on a more solid basis of fact, and were put forward 
with greater eloquence. 

It is worth while to study the thought of Claude Bernard more 
closely. Bernard was so subtle a thinker that it has always been 
difficult to classify him with any of the main currents of biological 
thought, but the following passage seems to me to sum up as well as 
any other the main shape of his ideas. "When a chicken develops in 
an egg", said he, "the formation of the animal body as a grouping of 
chemical elements is not what essentially distinguishes the vital force. 
This grouping takes place only according to laws which govern the 
physico-chemical properties of matter ; but the guiding idea of the 
vital evolution is essentially of the domain of life and belongs neither 
to chemistry nor to physics nor to anything else. In every living germ is 
a creative idea which develops and exhibits itself through organisation. 
As long as a living being persists it remains under the influence of 
this same creative vital force, and death comes when it can no longer 
express itself; here, as everywhere, everything is derived from the idea 
which alone creates and guides ; physico-chemical means of expres- 
sion are common to all natural phenomena and remain mingled 
pell-mell, like the letters of the alphabet in a box, till a force goes to 
fetch them to express the most varied thoughts and mechanisms. This 
same vital idea preserves beings by reconstructing the vital parts 
disorganised by exercise or destroyed by accident or disease. To the 
physico-chemical conditions of this primal development, then, we 
must always refer our explanation of life, whether in the normal or 
pathological state." Here Bernard seems to recognise the significance 
of universal teleology, for he says, "here, as everywhere, everything 


is derived, etc.", and at the same time he lays stress on the identifica- 
tion of the physico-chemical aspect with the scientific aspect, going 
on, indeed, to say that "physiologists can only act indirectly through 
animal physico-chemistry, i.e. physics and chemistry worked out in 
the field of life, where the necessary conditions of all living organisms 
develop, create, and support each other according to a definite idea 
and obedient to rigorous determinism". It is true that elsewhere he 
identifies this "force that goes to arrange the letters of the alphabet" 
with the "mediating nature" of Hippocrates and the archaeus 
faber of van Helmont. Had he read more in Lucretius than in 
Aristotle, he might rather have spoken of it as a necessary outcome 
of the constitution of nature, a suggestion more profoundly in 
harmony, perhaps, with the natural bent of the scientific conscious- 
ness (cf Bacon's remarks on Democritus in De Augmentis Scientiarum) . 
But, even so, he evidently regards it as the subject-matter of meta- 
physics and not of science, for he says in the next paragraph, "The 
term 'vital properties' is only provisional because we call properties 
' vital ' which we have not yet been able to reduce to physico-chemical 
terms, though doubtless we shall succeed in that some day". 

Organicism as an Occasion of Falling 

By making use of the thought of Bernard, we pass by an imper- 
ceptible transition from finalism and dynamic teleology to or- 
ganicism, another of the principal forms which the opposition to 
mechanistic biology has taken. This, like some of the other doctrines 
I have mentioned, has a long history behind it. The notion, "We 
murder to dissect", finds clear expression as early as a.d. 200, when 
Q^. Septimius Tertullianus, of Carthage, one of the Western Fathers, 
spoke thus of Herophilus, the Alexandrian anatomist, "Herophilus, 
the physician, or rather butcher, dissected 600 persons that he might 
scrutinise nature; he hated man that he might gain knowledge. 
I know not whether he explored clearly all the internal parts of man 
for death itself changes them from their state when alive, and death 
in his hands was not simply death, but led to error from the very process 
of cutting up". No more excellent statement of the organicistic view- 
point could be devised. Sir Kenelm Digby in 1644 gave a still 
clearer summary of this point of view, and even in the rationalistic 
eighteenth century there were scientific men who objected to the 
use of the term machine-like as applied to animals, and insisted that 

26 THE THEORY OF [pt. 

the living being was an organism. Cuvier took a very definite stand 
on this question when he said, "All the parts of a body are inter- 
related, they can act only in so far as they all act together; trying 
to separate one from the whole means transferring it to the realm 
of dead substance and entirely changing its essence". But the name 
most familiarly associated with biological organicism in this country 
is that of J. S. Haldane, who has frequently set forth his views upon 
this subject. His attitude is so well known that it need not be de- 
scribed here at any length, but, in brief, he points out that the living 
animal is an entity with a far higher degree of internal relatedness 
than any non-living system, and holds that the organic cannot 
be understood by a study of its parts though the inorganic very 
possibly can. In other words, an organism is an entity whose parts 
lose all their characteristic properties when they are studied away 
from the organism itself; they fall, as it were, into meaninglessness 
as soon as they are abstracted from the whole of which they are 
parts. Consequently that kind of physiology, and a fortiori biophysics 
and biochemistry, which analyses living organisms, is insufficient 
as an apparatus for understanding living things and should give 
place to studies in which organisms are regarded intact. Moreover, 
it is only in the untouched organism that those wonderfully well- 
balanced actions are seen by which the animal or plant holds to its 
own niche in the economy of nature, resisting every attempt to dis- 
lodge it, provided the attempt be not so successful as to disorganise the 
living thing. This power of maintaining a constancy in its external and 
internal environment is what Haldane regards as the deus ex machina, the 
property of living things essentially inexplicable by physico-chemical 
hypotheses and requiring special biological language for its formula- 
tion. (For a discussion of the "inconceivability argument" in bio- 
logy, see Mackenzie and Needham.) "All attempts", he says, "to 
trace the ultimate mechanism of life must be given up as meaningless. 
The aim of biology becomes a very different one — to trace in 
increasing detail, and with increasing clearness, the organic deter- 
mination which the organic conception formulates." It is to be 
noted, however, that Haldane vigorously criticised Drieschian neo- 
vitalism, adducing against it the argument of impossibility of inter- 
ference with the second law of thermo-dynamics, and the dubiousness 
of the theory of guidance without work done, a discussion of which 
on much better foundations was subsequently given by Lotka. 


Haldane was not convincing in his criticism of Driesch, and there 
can be little doubt that Driesch's position is a perfectly tenable one, 
provided its supporter closes his eyes to the nature of the scientific 
method on the one hand, and the actual history of recent scientific 
progress on the other. Another side of Haldane's teaching was the 
view that the living animal was in some way less abstract than the 
world of physics ; physics and biology, he thought, might some day 
coalesce, but it would then be found that physics would not have 
swallowed up biology; rather the contrary would occur and biology 
would swallow up physics. "The idea of life", he said, "is nearer 
to reality than the ideas of matter and energy, and therefore the 
presupposition of ideal biology is that inorganic can ultimately be 
resolved into organic phenomena, and that the physical world is thus 
only the appearance of a deeper reality which is as yet hidden from 
our distinct vision and can only be seen dimly with the eye of scien- 
tific faith." 

There had been precursory voices of all this in the nineteenth 
century, as when, in spite of the discoveries of Cagniard de Latour 
and others that the yeast-cell played an essential part in fermenta- 
tion, Justus von Liebig refused to credit them, fearing that their 
suggestions were a return to explanations by vital force. "Chemical 
actions may very well explain physiological actions, but certainly 
not vice versa ", said Moritz Traube. Claude Bernard, moreover, dis- 
cussed the matter with his usual subtlety. "Physiologists", he said, 
"must not forget that a living being is an organism with its own 
individuality. Since physicists and chemists cannot take their stand 
outside the universe they study bodies and phenomena in themselves 
and separately without necessarily having to connect them with 
nature as a whole. Physiologists, on the contrary, find themselves 
outside the animal organism which they see as a whole, even when 
trying to get inside so as to understand the mechanism of every part. 
The result is that physicists and chemists reject all idea of final causes 
for the facts which they observe while physiologists are inclined to 
acknowledge an harmonious and pre-established unity in an organised 
body, all of whose actions are independent and mutually generative. 
If we break up an organism for the sake of studying its parts it is only 
for the sake of ease in experimental analysis, and by no means in 
order to conceive them separately. Indeed, when we wish to ascribe 
to a physiological quality its value and true significance we must 

28 THE THEORY OF [pt. 

always refer it to this whole and draw our final conclusions only in 
relation to its effect on the whole. It is doubtless because he felt this 
necessary interdependence among the parts of an organism that 
Cuvier said that experimentation was not applicable to living beings 
since it separated organised parts that should remain united. For 
the same reason vitalists proscribe experiments in medicine. These 
views, which have their correct side, are nevertheless false in their 
general outcome and have greatly hampered the progress of science." 
Bernard did not commit himself to an absolutely unambiguous state- 
ment as to the correct and incorrect sides of organicism, and seems to 
have regarded it as true only in the sense that imaginative synthesis 
must follow radical experimental analysis. He was therefore quite 
opposed to that true and keen-edged organicism represented by 
Cuvier and other biologists, which denied the bare utility and 
legitimacy of the experimental analysis, and which was not un- 
justly satirised by Woolf in 1927: 

You cannot demonstrate the soul 

Except upon the animal as a whole; 

Spiritual autolytic changes begin 

As soon as you push a needle through the skin. 

Haldane's writings and those of his school, such as J. A. Thomson 
and G. G. Douglas, had extremely little effect on the direction taken 
by biological science in the first years of this century. As A. D. 
Ritchie pointed out, it is extraordinarily difficult to find out anything 
about living systems, unless their parts are treated in isolation, even 
if that be recognised as but the preliminary for imaginative synthesis, 
and, as many observers said, Haldane's own researches in the physio- 
logy of breathing afforded an excellent example of the usual scientific 
method. Biological research proceeded steadily on the usual lines, 
for Haldane's practical counsels could only be followed by those who 
were willing to abandon causal explanations in biology or to give 
up the hope of biology becoming an exact science. 

An influence was at hand, however, which was to lessen very much, 
if not to destroy altogether, the attraction of Haldane's opinions for 
biologists. A. N. Whitehead had in his earlier works, The Concept 
of Mature and The Principles of Natural Knowledge, elaborated his theory 
of extensive abstraction, but it was not until the publication of his 
Science and the Modern World that it began to exercise any wide- 


spread effect upon scientific men other than mathematical physicists. 
Whitehead boldly extended the concept of the organism to cover all 
objects, i.e. all events, non-living as well as living. The word "in- 
organic" would thus cease to apply to non-living nature and all 
physical systems would be regarded as in a sense incomprehensible, 
except when regarded as wholes composed of parts owing their very 
existence to their share and arrangement in the whole in question. 
Quoting Tennyson's, '"The stars', she whispers, 'blindly run'", he 
says, "An electron within a living body is different from an electron 
outside it, by reason of the plan of the body. The electron blindly runs 
within or without the body, but it runs within the body in accordance 
with the general plan of the body and this plan includes the mental 
state. But this principle of modification is perfectly general throughout 
nature, and represents no property peculiar to living bodies". 

Lloyd Morgan recognised in Whitehead's organisms his "systems 
of relations going together in substantial unity", which he had con- 
ceived of as stretching in degrees of ever vaster complexity from the 
smallest physical event to the universe itself. It was Lloyd Morgan, 
indeed, who pointed out first the significance of Whitehead's argu- 
ments for biological thought. He showed that the extension of 
organicism to cover the entire world of physics had no serious con- 
sequences for biological mechanists (who would continue to employ 
physico-chemical methods as before), provided that they had not 
adopted some form of scientific naturalism. At the same time, it 
could have little help for those who had insisted that the principal 
characteristic of living things was their organismic character, and 
had been led by this to propose far-reaching alterations in scientific 
logic or to give up the hope of causal explanation in biology. If, 
as it would seem, there are organisms everywhere, then the position 
that there are organisms nowhere turns out to be better placed than 
the position that living things are organisms and not other things ; 
for, in the former case, peace can be at once secured by attention 
to definitions, while in the latter case the irreducible characteristic 
of life is not organicism, whatever else it may be. The difference 
between the living and the non-living becomes a quantitative one, 
expressible in degrees of organisation. As has been pointed out, 
Haldane's prophetic observations concerning the eventual meeting- 
place of physics and biology have perhaps at last been justified, but, 
if so, with a barren benefit to neo- vitalism. 

30 THE THEORY OF [pt. 

Organicism and Emergence 

We may now pass by another small transition, from organicism 
to theories of emergence. Neo- vitalism in this form practically ceases 
to have any claim to the name, and approaches extremely closely 
to neo-mechanism. The principle of emergence in its simplest form 
is the statement that there are levels of existence in the universe, at 
each of which some more complicated form of being comes into 
existence, containing some essence absolutely new, and which could 
not have been predicted, even if all the properties of the constituents 
of the lower order had been known. This is evidently a conception 
very close to that of the organism, for just as the living or non-living 
system, looked at from one point of view, ceases to be itself as soon 
as it is dismembered, so the new level of complexity, looked at from 
one point of view, consists of lower levels of complexity joined together 
in a way that could not have been foreseen, because its properties 
and peculiarities are not the sum of the properties and peculiarities 
of its constituents. But it is important to note that there are here two 
parentheses, namely, "looked at from one point of view", implying 
that there is another point of view, and though the discussion is 
complicated here by the doubt as to whether Whitehead intends his 
organisms to be taken as a metaphysical theory, or as a scientific 
theory, yet in Lloyd Morgan the statement is clear that the emergent 
point of view has always a complementary one, the resultant point 
of view, "the emergent web and the resultant woof" as he calls it. 
This is really a new and more accurate way of putting the ancient 
antithesis of mechanism and teleology, for the scientific method in- 
volves the concept of resultance, since it continually seeks for the 
predetermining causes which must be in some way uniform with 
their effects, while the advent of something absolutely new at each 
level, i.e. atom to molecule, colloidal aggregate to living cell, etc., 
is a speculation hardly germane to science and resembling the final 

We find ourselves back again, then, at the distinction between 
metaphysics and science, which was first seriously studied by Kant. 
Most of the confusion has arisen in the past through an insufficiently 
clear decision as to the nature of biology. Biology cannot be philo- 
sophical and scientific, emergent and resultant, indeterminate and 
determinate, teleological and mechanical at one and the same time. 


No doubt the most powerful solvent of vitalism will turn out to 
be the set of changes now taking place in physics. It is as yet too 
early to describe very definitely the effects of these, and several 
modern writers on the subject are rather free in their use of the word 
"mysticism", but it is at any rate clear that physicists are coming to 
see more clearly than before the impHcations and the limitations of 
the study of the metrical aspects of the world, which is what science is. 
Behind these sets of numbers and quantities the background of the 
world is enigmatic, and Heisenberg's Principle of Indeterminacy 
indicates that extreme accuracy can only be obtained at a cost. 
Again, the abandonment of the model in physics is a highly important 
step, and physics seems to have reached a point at which there is no 
analogy in our everyday experience for the phenomena with which 
it is dealing, so that we cannot even picture in ordinary words what 
is happening. Eddington, in his great work The Nature of the Physical 
World, also shows that physics no longer speaks of the motion of 
every individual particle in the universe being rigidly determined but 
rather of the relative probabilities of its motions, i.e. the odds on 
them. If this funeral of Laplace's Calculator should turn out to 
be enduring, a good deal of difficulty may vanish from the biological 
sphere. But I should prefer to leave the working out of these possi- 
bilities to those better qualified than myself, and to suggest simply 
that if the mechanical theory of the world is being reconstructed by 
modern physics, there may be a widespread sapping of the force of 
neo-vitaHstic contentions in the near future. I have often thought 
that neo-vitalists were thinkers whose religious sense had got into the 
wrong place; unable to set up commonsense watertight compart- 
ments on the one hand, or to work out a philosophy of the forms of 
experience on the other, they brought the numinous into biology and 
abused biophysics. The fundamental contention of the mechanists 
always was that science and the scientific method were one and that 
biology was complicated physics — this remains unaltered. But if 
physics is more and more obviously throwing off the links which 
bound it in the past to metaphysical materiahsm, and admitting 
itself to be the study of the metrical aspects of the world, there will 
be perhaps less excuse for the misplacement of the numinous, as it 
might be called; and the affirmation that biology must be based 
upon physics will cause less antagonism than in the past. In a word, 
the vitaHsts wished to introduce mysticism at the wrong level; the right 

32 THE THEORY OF [pt. 

level would seem to be, as it were, underneath the metrical abstrac- 
tions of physics, i.e. outside science altogether, and if this is realised, 
the vitalist and the mechanist will fuse into one and the same 
person — a happy consummation. It is curious that at the present 
time, when physics is so markedly freeing itself from scientific 
naturalism, biologists are sometimes found to support that untenable 
world-view, while still farther away from the inorganic world, 
literary criticism tries to make itself modern by using a psychological 
jargon, and applying to its problems all the rigour of a materialist 

Neo-mechanism as a Theory for Chemical Embryology 

The principal philosophical obstacles to physico-chemical embryo- 
logy have now been assessed and nothing remains but to outline its 
own theoretical basis. Anyone who was dissatisfied twenty years ago 
with the various forms of neo-vitalism which have already been 
discussed would have had no alternative but to accept the simple, 
though rather incredible, scientific naturalism of the preceding 
century, unless, indeed, he was acquainted with German philosophy, 
and understood the momentous consequences which flowed from the 
apparently technical question, "How are a priori synthetic judgments 
possible?" The varieties of neo-vitalism may perhaps be thought of, 
in so far as they are not modern forms of difficulties which have 
for many centuries perplexed philosophers, as a series of reactions 
against mechanistic biology insufficiently distinguished from scientific 
naturalism. This confusion is well seen in the earlier phases of the 
American discussion which led up to the symposium of 191 8. It is 
often difficult to tell, as in the papers of Nichols; Ritter; More and 
Fraser Harris, whether the writer is attacking the mechanical theory 
of the universe regarded as an ultimate metaphysical faith or the 
mechanical methodology of science. 

Before the eighteenth century, of course, there had always been 
thinkers who felt the necessity of including both teleology and its 
antithesis in their systems of thought. This pull in two directions 
accounts for those very interesting mediaeval theologians, such as 
Siger of Brabant and John of Jandun, who wished to acknowledge 
two kinds of truth, theological and philosophical (see Maywald and 
Gilson). A right balance had to be struck in some way between 
Democritus and Plotinus, and in the seventeenth century, for in- 


stance, Sir Thomas Browne wrote to his son advising him to study- 
Lucretius yet not to read too much in him, "there being divers 
impieties in him". Perhaps the greatest figure in this line of descent 
is the Cardinal Nicholas of Cusa, who, in his book De Docta Ignorantia 
of 1440, contended that the principle of contradiction was only valid 
for our reason, and so foreshadowed Kant and Hegel (cf. Vansteen- 
berghe) . But the starry heavens with their infinite spaces that terrified 
Pascal and their mechanical order and metrical uniformity revealed 
by Kepler and Copernicus, on the one hand, and the moral law 
with its tremendous purposiveness and its theological implications, 
on the other hand, were never really faced at one and the same 
moment and taken seriously together until the time of Kant, who 
first subjectivated what had before struggled in the external world, 
and suggested that the contradictions of our thought might spring 
from the constitution of our own intelligence. "It has always been 
assumed", he said, "that all our knowledge must conform to objects. 
The time has now come to ask, whether better progress may not be 
made by supposing that objects must conform to our knowledge." 

Omnis enim longe nostris ab sensibus infra 
primorum natura jacet. . . 

Lucretius had said, but Kant went farther, and suggested that our 
intelHgence can help us no more than our senses in the attempt 
to see things as they really are. 

This was the great service that Kant performed for philosophy, and 
in the light of it the scientific mind was relieved of the burden of 
having to believe finally in its own account of the world. But in the 
scientific controversies of the last century, Kant was forgotten, and 
the continual successes of the scientific method led to a naturaUstic 
outlook, which was wholly unsatisfactory. It had been supported by 
T. H. Huxley, Herbert Spencer, W. K. CUfford, Tyndall, Ray 
Lankester, and many others: it apparently still is by Chalmers 
Mitchell. But, as a widely accepted attitude, it did not live long into 
the present century, and from such blows as James Ward's Naturalism 
and Agnosticism and Antonio Aliotta's The Idealistic Reaction against 
Science, it never recovered. Physico-chemical biologists were thus left, 
as it were, without visible means of support, and existed for some time 
on a purely pragmatic basis, devoid of any epistemological comfort. 
Gradually, however, a more satisfactory attitude came into being. 

34 THE THEORY OF [pt. 

Karl Pearson pro\-ided an intimation of it when he remarked, 
"Those who say that mechanism cannot explain life are perfectly 
correct, but then mechanism does not explain anything. Those, on 
the other hand, who say that mechanism cannot describe hfe are 
going far beyond what is justifiable in the present state of our know- 
ledge". A clear enunciation of it, informed with the charm of all 
his writings, was given by d'Arcy Thompson in the .\ristoteUan 
Society^ S\Tnposium of 191 8. "In the concepts of matter and energy", 
he said, " the Whole is not enshrined, mechanism is but one aspect 
of the world. These are the proper categories of objective science, 
but they are no more: the physicist is, ipso facto, a mechanist, but he 
is not by impHcation a materialist; nor is the biologist of necessity 
a materiahst, even though he may study nothing but mechanism in 
the material fabric and bodily acti\ities of the organism." R. S. 
Lillie's paper of 1927 might be taken as one of the best expositions 
of this point of \-iew. "Every biologist is aware", he says, "in his 
non-professional moments that the possibiUties of hfe are larger than 
the mechanistic \iew impHes. This is only another way of acknow- 
ledging that the whole mechanistic conception is an incomplete, 
derivative, or abstract one. To regard it as philosophically final is a 
grave mistake." Thus Lillie remains cominced of the adequacy of 
physico-chemical biologv', but expressly repudiates the elevation of 
mechanism into a metaphysic. 

LilUe goes on to discuss the abstract, distorted and incomplete 
character of the world which is presented to us by the employment 
of the scientific method. "To say", he proceeds, "that Hfe is 'nothing 
but' a combination of chemical reactions in a colloidal substratum 
is unscientific. Life may be and apparently is that in part but to 
regard any such scientific formulation as a complete and adequate 
representation of its total reaUt}- is simply to misconcei\-e the structure 
of science." This is well said; Ufe is indeed a "dynamic equihbrium 
in a polyphasic system", but also "Life is a manifest of emergent 
creativity", "Life is a pure flame and we five by an imisible sun 
within us", "Life is a sad composition, we five with death and die 
not in a moment", and — if you will, 

Life, like a dome of many-coloured glass, 
Stains the white radiance of eternity 
Until death tramples it to fi-agments. 


"The dilemma of vitalism is irresolvable", says Lillie, "so long as 
we regard the units, concepts, and formulae found vaHd in physical 
science not as abstractions but as primary and self-existent reaUties, 
by a combination of which all the properties of living beings as of 
other natural phenomena can be derived." 

In a former discussion I contrasted what might be called the 
Democritus-Holbach-Huxley attitude in biology with the Driesch- 
Haldane-Russell-Rignano attitude, and concluded after examining 
them that both involved insuperable difficulties. Lotze was the 
philosopher to whom I went for help in the elaboration of a better 
standpoint. "The true source of the life of science", said he, "is to 
be found, not indeed in admitting now a fragment of one view and 
now a fragment of the other, but in showing how absolutely universal 
is the extent and at the same time how completely subordinate is 
the significance of the mission which mechanism has to fulfil in the 
structure of the world." And in another place, "We granted v^aUdity 
to the mechanical view in so far as concerns the examination of the 
relations between finite and finite and the origin and accomplish- 
ment of any reciprocal action whatever; we as decidedly denied its 
authority when it claimed acceptance, not as a formal instrument of 
investigation, but as a final theorv' of things". "Nowhere is me- 
chanism", says Lotze, "the essence of the matter, but nowhere does 
being assume another form of finite existence except through it." 

I went on to argue that, although Lotze made everv^ effort to demon- 
strate how mechanism and teleolog)' could fit together in the universe, 
he failed to do so convincingly, and that it was more satisfactory to 
make them necessary results of the a priority of our ways of thought. 
"We may regard", I said, "the mechanistic view of the world as a 
legitimate methodological distortion, capable of appHcation to any 
phenomenon whatever, and possessing no value at all as a meta- 
physical doctrine." Mechanism, whichever of its forms ^defined by 
C. D. Broad, M. R. Cohen and Y. H. Krikorian turns out to be 
the minimum requirement of science, is, in fact, not metaphysical 
materiahsm. It is necessary to maintain it on methodological grounds, 
but it is pernicious to allot it any v\ider value. It stands, in fact, 
as one of the kinds of way in which the human spirit reacts to the 
universe in which it finds itself, and it springs, as R. G. CoUingwood 
puts it, directly from the ultimate root of all science, the assertion 
of the abstract concept. "He who generaUses is an idiot", said 


36 THE THEORY OF [pt. 

William Blake, but that was a revelation of the poetic or the religious 
mind. The scientific spirit is as profound as these, but it sets out 
upon a different path from the very beginning and reaches in the 
end a country different in every way. It directs its interest from the 
first to the correlation of differences between phenomena rather than 
to individual phenomena themselves, and the impulse to classify 
leads inevitably to the supremacy of the mechanical cause and the 
mathematical formula. It stands "at diameter and sword's point" 
with such aphorisms as "Everything is itself and not something else" 
or "Nothing is ever merely anything". 

R. G. Collingwood has expressed this in a memorable passage: 
"Mathematics, mechanics, and materialism are the three marks of 
all science, a triad of which none can be separated from the others, 
since in fact they all follow from the original act by which the scientific 
consciousness comes into being, namely, the assertion of the abstract 
concept. They are all, it may be said, products of the classificatory 
frame of mind, corollaries from the fact that in this frame of mind 
the universal and the particular are arbitrarily separated and the 
universal asserted in its barren an'd rigid self-identity. It is this 
barrenness and this rigidity which confer their character upon the 
doctrines of scientific materialism. Hence it is idle to imagine that 
materialism is justified in some sciences and not in others. It is idle 
to protest that science ought to surrender its materialistic prejudices 
when it finds itself face to face with a non-material object such as 
the soul. No object is material, in the metaphysical sense of the word, 
except in so far as scientific thinking conceives it so; for materiality 
means abstractness, subjection to the formulae of mechanical deter- 
mination and mathematical calculation, and these formulae are 
never imposed upon any object whatever except by an arbitrary 
act which falsifies the object's nature. This only appears paradoxical 
when we fail to see the gulf which separates the common-sense 
materiaHty of a table, its sensible qualities, from its metaphysical 
materiality, the abstract conceptual substrate of those qualities. It is 
this substrate whose transcendent or abstract existence is asserted by 
materialism. Hence we cannot distinguish objects like tables which 
are really 'material' from objects in whose presence science must 
unlearn its materialistic habits of thought. MateriaHsm is no more 
the truth in physics than in psychology, and no less. It is the truth 
about any object, just in so far as this object is by abstraction re- 


ducible to terms of pure mathematics; and no object is so reducible 
except by consciously or unconsciously shutting our eyes to every- 
thing which differentiates it from anything else. This conscious or 
unconscious act of abstraction is the very being of the scientific con- 
sciousness; and it is therefore no matter for pained surprise when 
science shows a bias towards determinism, behaviourism, and 
materiaHsm generally". 

By this time the general outlines of this theoretical excursus should 
have become clear. Embryology, to put it plainly, has been for so 
many years the happy hunting-ground of vitaHstic and neo-vitalistic 
theory that the first treatise on the physico-chemical aspect of it 
could hardly go without some kind of theoretical introduction. 
"VitaHstic conceptions", said Claude Bernard in 1875, with the 
voice of authentic prophecy, "can no longer hover over physiology 
as a whole. The developmental force of the egg and the embryonic 
cells is the last rampart of vitalism, but in taking refuge there, it 
transforms itself into a metaphysical concept and snaps the last link 
connecting it with the physical world, and the science of physiology." 

It is to be hoped that what has now been said will place in a right 
light the aims of physico-chemical embryology, and provide it, as 
it were, with its decretals. That they are not false will be the hope 
of every exact biologist. 

Chemical embryology is now indeed at a critical point in its 
history. On the one hand, it links up with the morphological work 
of the classical embryology and the experimental work of the 
Entwicklungsmechanik school, while on the other hand it has 
affinities with genetics, a science which is every day becoming more 
physiological and which will more and more seek for the effects 
of its factors in the biochemistry of development. Goldschmidt's 
book, and the work of Dunn, who found a lethal gene in an inbred 
strain of fowl which caused a regular chick mortaUty at the seven- 
teenth day of incubation, are important examples of this. Another 
relationship of chemical embryology is to obstetric medicine, for such 
problems as the toxaemias of pregnancy will not be solved by Hippo- 
cratic observation unassisted by a knowledge of the chemistry of 
the embryo and the placenta. The attention devoted by the Medical 
Research Council to such problems is an acknowledgment of this 
fact. Nor is veterinary physiology in a position to do without the 
aid of chemico-embryological researches, as is shown by the incident 


of the myxoedematous pig foetuses of western America in the work 
of Smith. 

But all practical applications, how valuable soever, must give 
place to the increase of knowledge itself, and therefore the physico- 
chemical history of embryonic development, from the egg-cell to the 
loosing of the individual into the activity of post-natal life, is to be 
the theme of this present book. "The history of a man for the nine 
months preceding his birth", said S. T. Coleridge, "would probably 
be far more interesting, and contain events of far greater moment 
than all the three-score and ten years that follow it." 






Nobilissimo juveni Medico Philippo 

de Glarges, amicitiae ergo libenter 

Gulielmus Harveus scripsit, Anglus, 

Med. Reg. et Anat. Prof. Londin. 

Mai. 8 1641 

From the commonplace book of 
Philip de Glarges. 

Not to prayse or disprayse : all did well. 

William Harvey's MS. notes, 
Canones Anatomiae Generalis, 6. 


It is open to anyone to say with some appearance of truth that 
physico-chemical embryology has no history, since the attempt to 
unravel the causes of embryological phenomena by physico-chemical 
means has only recently begun. But such a statement would betray 
a superficial and jejune mentality. Physico-chemical embryology has 
its roots in the history of embryology as a whole, and it is those roots 
which I shall try to uncover in what follows. It must be remembered 
that morphological must theoretically precede biophysical analysis, 
as it has actually preceded it chronologically, and to that extent 
physico-chemical embryology cannot be properly understood without 
reference to its descriptive husks, and their historical growth. More- 
over, even in antiquity there are hints that the chemistry of the 
embryo was dimly envisaged (as in Aristotle, see p. 70). Again, that 
philosophical problem which we have already considered, plays a great 
part in the history of embryology, and as we watch the pendulum swing- 
ing from Democritus to Aristotle, back again over to Herophilus, 
and back once more to Galen, we almost feel as if we were spectators 
looking on, like Hardy's spirits, at a great drama, with the movement of 
which we are powerless to interfere, but knowing that the existence of 
exact biology depends upon which side wins. Lastly, such unmorpho- 
logical questions as the respiration and nutrition of the embryo were 
discussed from the most ancient times, and it is surely no unduly wide 
interpretation of the word which leads us to include an account of 
these opinions under the heading of chemico-embryological history. 
Nor could the present moment be more appropriate for such an 
historical survey. Embryology is entering a new phase: and on the 
threshold it is very fitting that some retrospective attention should 
be paid to the phases which it has already passed through. The 
events of the past, moreover, throw Hght on those of the future, and 
this is true not necessarily in Spengler's sense but also because the 
historical approach to problems actually unsolved protects them, 
by a kind of gentle scepticism, from too severe a subjection to doc- 
trinaire presentations. "Die Geschichte einer Wissenschaft ist der 
Hort ihrer Freiheit; sie duldet ihr keine einseitige Beherrschung", 
said Louis Choulant in 1842. Theoretical bhnd alleys, such as the 
final cause, practical blind alleys, such as preformationism and 
phlogiston, are always able to remind us that we may be mistaken. 


No exhaustive treatise on the history of embryology at present 
exists. The nearest approach to it is the very valuable memoir of 
Bruno Bloch with its epitome but this only covers the era of the 
Renaissance with thoroughness. Hertwig's account, which he printed 
at the beginning of his great Handbuch der Entwicklungslehre, does not 
deal very fully with any aspect of the subject before 1800, nor do 
the much shorter ones of Henneguy and Minot. The latter paper is 
interesting in that it ends with an emphasis on the need for a physico- 
chemical attitude in the future. The introduction to Keibel's book 
is much slighter, but contains some useful information. There are 
various monographs and papers on special points, such as Pouchet's 
rather untrustworthy treatment of the embryology of Aristotle, and 
Lones' discussion of it, which is worse. Camus' notes are still the best 
commentary on the Historia Animalium. Again, useful information on 
some cultural points is to be had from the treatise of Ploss & Bartels. 
The introductions to certain books also contain valuable information, 
and in this class comes Dareste's remarkable book on teratology. 
The bibliographies contained in v. Haller's eighth volume and in 
Heffter's book, are, naturally, of the greatest assistance. 

These reservations made, the principal reviews of the subject are 
chiefly to be found in histories of science in general, such as Sarton's; 
histories of biological theory, such as Radl's; histories of obstetrics, 
such as V. Siebold's, Spencer's and Fasbender's; histories of gynaeco- 
logy, such as McKay's; and histories of anatomy, such as Singer's 
and V. Toply's. Histories of medicine as a whole are numerous 
and helpful: I have found those of Garrison and Neuburger- 
Pagel most useful. Those which deal with special periods are also 
of assistance, such as Schrutz and Browne on Arabian, Bloch on 
Byzantine, and Harnack on Patristic medicine. Histories of chemistry 
provide no help, for ancient chemistry was so oriented towards 
"practical" results, such as the lapis philosophorum and elixir vitae, 
that the egg was only considered as a raw material for various 
preparations. The investigation of its change of properties during 
the development of the embryo did not occur to the alchemists. 
Detailed studies of particular subjects, such as those contained in 
Singer's two excellent volumes The History and Method of Science, 
may also be of some assistance. Again, there are books which give 
a wonderful orientation and an articulate survey of vast tracts : of 
these Clifford Allbutt's Greek Medicine in Rome, with its mass of 
references, is among the most valuable. And Miall's Early Naturalists 


must not be omitted, for, apart from the peculiar charm of style which 
marks it, it contains some singularly helpful bibliographical data. But 
the study of the original sources, so far as that is possible, is a duty 
which cannot be avoided, and in what follows I have been careful 
to copy down no statement from a previous review when it was 
possible to read the actual words of the writer himself. 

This practice of going to the originals is made peculiarly necessary 
in a case such as the present one, when the history of a subject is 
to be regarded from an entirely new angle. My intention is to give 
here the sketch of a history of embryology consistently from the 
physico-chemical angle, and to show, at one and the same time, how 
our knowledge of the development of the embryo has come into being, 
and how throughout the process what we now call the physico- 
chemical foundations of embryonic growth have from time to time 
received attention, even though it was largely speculative. Since few 
have previously examined the history of the subject, and none from 
this angle, I have in many cases come upon interesting facts which 
have remained unknown owing to the very attitude of mind pre- 
viously adopted. 

Finally, I would defend the arrangement of my Sections only on 
the ground that it is suitable in the present state of historical know- 
ledge. I say little about embryology in ancient China and ancient 
India, because on the basis of what we know there is little to say, 
not because it was intrinsically less interesting than the embryology 
of Mediterranean antiquity and the later West, though this may turn 
out to be the case. I do not propose a framework for historical facts 
in what follows ; I only attempt to bring them together, and to reveal 
some of the relationships between them. If the traditional frame- 
work turns out to be badly constructed — and there are many signs 
that it may — the facts can be rearranged. 

The history of single forms of scientific knowledge is in a way 
happier because containing more of continuity than that of civilisa- 
tion as a whole. The assiduity with which men of different periods 
in the rise and decHne of a culture pursue the different forms of 
human experience may, as Spengler has shown, vary much, but those 
forms remain fundamentally the same, even if their manifestations 
are profoundly changed. That science, at any rate, does maintain 
some sort of continuity whatever gaps there may be between the 
phases of its progress, is a belief agreeable with all the available facts, 
and one which no criticism will easily shake. 



I -I. Non-Hellenic Antiquity 

Since biological science as a whole was little cultivated in ancient 
Egypt and the ancient civilisations of Babylonia, Assyria and India, 
the study of embryology, we may assume, was equally little pursued. 
Doubtless the undeveloped embryo, 
whether in egg or uterus, carried 
with it, for these persons of remote 
antiquity, some flavour of the ob- 
scene in the literal sense of the word. 
But embryology stands in a peculiar 
relation to the history of humanity, 
in that even at the most remote times 
children were being born, and, 
though the practitioners of ancient 
folk-medicine might confine their 
ideas for the most part to simple 
obstetrics, they yet could hardly 
avoid some slight speculation on the 
growth and formation of the embryo. 
Fig. I illustrates this level of culture. 
It is a painted and carved door from 
a house in Dutch New Guinea, taken 
from de Clercq's book; the original 
was of yellowish brown wood. The 
male embryo is clearly shown, but 
the artist evidently had a hazy con- 
ception of the umbilical cord. The 
line passing from the uterus to the head may or may not be merely 
ornamental. The movement of the foetus in utero played and still 
plays a large part in the folklore of primitive peoples, as may be read in 
the exhaustive treatise of Ploss & Bartels. For information concerning 
god-embryos in primitive religion see Briffault. 

Ancient Indian embryology achieved a relatively high level. 
Structures such as the amniotic membrane are referred to in the 


I . Painted and carved door from 
New Guinea (de Clercq). 


Bhagavad-Gitd. Susriita believed that the embryo was formed of a 
mixture of semen and blood, both of which originated from chyle. 
In the third month commences the differentiation into the various 
parts of the body, legs, arms and head, in the fourth follows the 
distinct development of the thorax, abdomen and heart, in the sixth 
are developed hair, nails, bones, sinews and veins, and in the seventh 
month the embryo is furnished with any other things that may be 
necessary for it. In the eighth there is a drawing of the vital force 
to and from mother and embryo (is this comparable with the 
Hippocratic eXKeiv? see Peck) which explains why the foetus is not 
yet viable. The hard parts of the body are derived from the father, 
the soft from the mother. Nourishment is carried on through vessels 
which lead chyle from mother to foetus. (For further details see 
Vullers.) Ancient Chinese embryology was very similar, if we 
may judge from Hureau de Villeneuve; Maxwell & Liu and von 

Egyptian medicine did not venture on embryological speculation, 
or so it would seem from the writings which have come down to 
us — the Ebers medical papyrus does not once mention the embryo 
(Brugsch) . But there are points of interest as regards Egypt in this 
connection. The Egyptians were responsible for one of the greatest 
helps in systematic embryological study, namely, the discovery of the 
artificial incubation of the eggs of birds. The success of this process was 
to have so obvious an effect on embryology and the abortive attempts 
to bring it to completion were so frequent in the West right up to 
the nineteenth century a.d. that it is remarkable to find artificial 
incubation practised "probably", in Cadman's words, "as far back 
as the dawn of the Old Kingdom, about 3000 B.C." It is doubtful 
whether the very remote date could be supported by Egyptological 
evidence, for, according to Hall and Lowe, hens were not introduced 
into Egypt from Mesopotamia or India until the time of the eighteenth 
dynasty {ca. 1400 b.g.) when there was much intercourse with the 
East (cf Queen Tiy and the Tell-el-Amarna correspondence) : before 
then the Egyptians had only goose or duck's eggs. Artificial incubation 
is certainly as old as Diodorus Siculus and Pliny, for both of them 
refer to the practice, the latter in connection with a curious piece of 
ancient sympathetic magic. " Livia Augusta, theEmpresse," says Pliny, 
"wife sometime of Nero, when she was conceived by him and went 
with that child (who afterwards proved to be Tiberius Caesar) being 


very desirous (like a yong fine lady as she was) to have a jolly boy, 
practised this girlish experiment to foreknow what she should have 
in the end; she tooke an egge, and ever carried it about her in her 
warme bosome; and if at any time she had occasion to lay it away, 
she would convey it closely out of her own warme lap into her 
nurses for feare it should chill. And verily this presage proved true, 
the egge became a cocke chicken, and she was delivered of a sonne. 
And hereof it may well be came the device of late, to lay egges in 
some warme place and to make a soft fire underneath of small straw 
or light chaffe to give a kinde of moderate heate ; but evermore the 
egges must be turned with a mans or womans hand, both night and 
day, and so at the set time they looked for chickens and had them" 
(Philemon Holland's translation). 

Pliny also says, "Over and besides there be some egs that will 
come to be birds without sitting of the henne, even by the worke 
of Nature onely, as a man may see the experience in the dunghills 
of Egypt. There goeth a prettyjeast of a notable drunkard of Syracusa, 
whose manner was when hee went into the Taverne to drinke to lay 
certaine egges in the earth, and cover them with moulde, and he 
would not rise nor give over bibbing untill they were hatched. To 
conclude, a man or a woman may hatch egges with the very heate 
onely of their body". This story occurs also in Aristotle. 

The Emperor Hadrian — curiositatum omnium explorator as Tertullian 
calls him — writing in a.d. 130 to his brother-in-law, L. Julius 
Servianus, from Egypt, says, "I wish them no worse than that 
they should feed on their own chickens, and how foully they hatch 
them, I am ashamed to tell you". In the Description de VEgypte, 
written by the members of the scientific staff of Napoleon's Egyptian 
expedition, and published at Paris in 1809, Roziere and Rouyer 
wrote on the artificial incubation of the Egyptians. They conjecture 
very probably that the Emperor was shocked owing to a misunder- 
standing shared by Aristotle, PUny, de Pauw and Reaumur, namely, 
that the "gelleh" or dung was used to heat the eggs by its fermenta- 
tion, and not, as is and was actually the case, by being slowly burnt 
in the incubation ovens. Bay gave an account of the ovens in modern 
times, but the best one is that of Lane. "The Egyptians", said Lane 
in 1836, "have long been famous for hatching fowls' eggs by artificial 
heat. This practice, though obscurely described by ancient authors, 
appears to have become common in ancient Egypt from an early 


(from Cadman) 

(from King) 


time. In Upper Egypt there are over fifty establishments, and in 
Lower Egypt more than a hundred. The furnace is constructed of 
sun-dried bricks and consists of two parallel rows of small ovens and 
cells for fire divided by a narrow vaulted passage, each oven being 
about 9 or 10 feet long, 8 feet wide and 5 or 6 feet high, and having 
above it a vaulted fire-cell of the same size but rather less in height. 
The eggs are placed upon mats or straw, one tier above another 
usually to the number of three tiers and the burning fuel is placed 
upon the floors of the fire-cells above. The entrance of the furnace is 
well closed. Each furnace consists of from twelve to 24 ovens and 
receives about 150,000 eggs during the annual period of its con- 
tinuing open, one quarter or one third of which generally fail. The 
peasants supply the eggs and the attendants examine them and after- 
wards generally give one chicken for every two eggs that they have 
received. The general heat maintained during the process is from 
100 to 103 of Fahrenheit's thermometer. The manager, having been 
accustomed to the art from his youth, knows from long experience 
the exact temperature that is required for the success of the operation 
without having any instrument like our thermometer to guide him. 
The eggs hatch after exactly the same period as in the case of natural 
incubation. I have not found that the fowls produced in this manner 
are inferior in point of flavour or in other respects to those produced 
from the egg in the ordinary way." The accompanying picture 
(Plate I a), taken from Cadman, shows the interior of a modern 
peasant's incubator. There is reason to beheve that its construction 
and operation vary very little, if at all, from that of the ovens used in 
dynastic Egypt. 

When Bay visited the native incubators in 191 2 he took with him 
a flask of lime water and a thermometer. The former showed a large 
precipitation of calcium carbonate and the latter stood at 40° C. He 
was led to speculate on the value of a high CO2 tension in the at- 
mosphere, and concluded that it must have a beneficial effect, since 
the loss in the native incubator was not more than 4 per cent., while 
that in the oil-heated agricultural incubators of his time was as 
much as 40 per cent. Cadman, writing in 1921, suggests that the 
well-known non-sitting instinct of Egyptian poultry is an effect of 
the ancient practice of artificial incubation. But enough has been 
said of the Egyptian "Ma'mal al katakeet", or chicken factory. 
In spite of the remarkable opportunity thus afforded for acquiring 


facts in experimental embryology, no use was apparently ever made 
of it, though there seems to be a certain amount of traditional 
information current among the peasant operators, as, for example, 
that the "ruh" or life enters into the egg at the eleventh day. It 
w^ould be interesting to investigate this aspect of the subject further. 

In ancient China also it would appear that artificial incubation 
was successfully carried on in remote antiquity, if we may judge by 
the account given by King. Native incubation in China is carried 
on in wicker baskets, heated with charcoal pans (Plate Ib). The 
attendants sleep in the incubator itself, and use the same thermometer 
as the Egyptians, namely, their eyelids, to which they apply the blunt 
end of the egg. The Egyptian success was known generally in the 
West in later times though it could not be imitated. ' ' The Aegyptians ' ' , 
said Sir Thomas Browne, "observed a better way to hatch their 
Eggs in Ovens, than the Babylonians to roast them at the bottom of 
a sling, by swinging them round about, till heat from motion had 
concocted them; for that confuseth all parts without any such effect." 
Browne's slightly rueful tone suggests that he tried it himself. It is 
interesting that this quaint experiment was the cause of a controversy 
between Sarsi, who asserted on the authority of Suidas that it was 
possible, and GaHleo, who thought the idea ridiculous. Modern work 
on the instability of albumen solutions, such as that of Harris, lends 
some colour to the legend. (See p. 275.) 

Ancient Egypt supplies the starting-point for another and pro- 
founder train of thought which recurs constantly throughout the 
history of embryology, and to which I shall have to refer again more 
than once. This was concerned with the problem of deciding at what 
point the immortal constituent universally regarded as existing in 
living beings took up its residence in the embryo. Some fragments 
of ancient Indian philosophy assure us that the Vedic writers occupied 
themselves with this question, and according to Crawley the Avesta 
theorises upon it. But as early as 1400 B.C., i.e. during the eighteenth 
dynasty in Egypt, something was said regarding this, for we have 
extant at the present day a very beautiful hymn to the sun-god, 
Aton, written by no less a person than Akhnaton (Nefer-kheperu-Ra 
Ua-en-Ra, Amen-hetep Neter heq Uast), generally known as 
Amenophis IV or the "heretic" king, who abandoned the traditional 
worship of the Theban god Amen-Ra and established an Aton-cult, 
as has been described by Baikie and others. One of his hymns, which 


bears considerable resemblance to the one hundred and fourth 
psalm, runs as follows (in Breasted's translation) : 

{the sun- god is addressed) 

Creator of the germ in woman, 

Maker of seed in man, 

Giving life to the son in the body of his mother, 

Soothing him that he may not weep, 

Nurse (even) in the womb. 

Giver of breath to animate every one that he maketh 

When he cometh forth from the womb on the day of his birth. 

Thou openest his mouth in speech. 
Thou suppliest his necessity. 

When the fledgling in the egg chirps in the shell 
Thou givest him breath therein to preserve him alive. 
When thou hast brought him together 
To the point of bursting out of the egg, 
He cometh forth from the egg 
To chirp with all his might. 

He goeth about upon his two feet 
When he hath come forth therefrom. 

The important point here is that life = soul. At this early period 
there is no trace of the notions which appear later, such as the idea 
that embryos are not aUve until the time of birth or hatching, or 
the idea that the soul is breathed into the embryo at some particular 
point in development. But in later times these considerations carried 
great weight, and with the rise of theology a definite stand had to 
be taken about them, for otherwise no ethical status could be assigned 
to abortion. Speculation on these matters has continued without 
cessation since the time of Akhnaton, reaching a climax perhaps in 
Christian times with Cangiamilla's Embryologia Sacra, and living on 
embedded in Roman Catholic theology up to our own era. In the 
last century the subject seems to have had a special fascination for 
Ernst Haeckel, who frequently mentioned it. But the future holds no 
place for the discussion of such themes, and what has been called 
"theological embryology" is already dead, though we may perhaps 
descry its successor, psychological embryology, in such researches as 
those of Teuscher, Cesana, y Gonzalez, Swenson and Coghill. 


Ancient Greek thought shows many evidences of appreciation of 
the mystery of embryonic growth, as for example 
in the Orphic cosmogonies, which had their origin 
about the seventh or eighth century b.g. In these 
rehgious and legendary descriptions of the world, 
which have been exhaustively discussed by A. B. 
Cook and F. Lukas, the cosmic egg plays a large 
part, and has been shown to occur also in the . ^ , , . 

. • f T^ T 1- -r. • 1 Fig- 2. Eros hatching 

ancient cosmogonies ot Lgypt, India, Persia and from the cosmic egg. 
Phoenicia. A familiar reference to this cosmic (A Hellenistic gem de- 
egg, out of which all things were produced at ^^^^ ^ y . . oo .j 
the beginning of the world, is in Aristophanes' comedy. The Birds, 
where the owl, as leader of the Chorus, says in the Parabasis 
(J. T. Sheppard's translation) : 

Chaos was first, and Night, and the darkness of Emptiness, gloom 

tartarean, vast ; 
Earth was not, nor Heaven, nor Air, but only the bosom of Darkness ; 

and there with a stirring at last 
Of wings, though the wings were of darkness too, black Night was inspired 

a wind-egg to lay. 
And from that, with the turn of the seasons, there sprang to the light 

the Desired, 
Love, and his wings were of gold, and his spirit as swift as the wind when 

it blows every way. 
Love moved in the Emptiness vast, Love mingled with Chaos, in spite of 

the darkness of Night, 
Engendering us, and he brought us at last to the light. 

And perhaps another reference to the place of the egg in ancient 
cosmogony occurs in The Arabian Nights, where Aladdin's request 
for a roc's egg is treated as a blasphemy by the genie. Still more 
fantastic is the speculation of C. H. Rice (in Psyche, 1929!) that the 
world is an egg; living matter being the embryo and inorganic 
matter the yolk. But none of the facts which have so far been 
mentioned bears more than obliquely upon the main centre of 
interest, the study of embryology. For its direct ancestry, Greece, as 
might be expected, is responsible. 

1-2. Hellenic Antiquity: the Pre-Socratics 

The pre-Socratic philosophers nearly all seem to have had opinions 
upon embryological phenomena, many of which are worth referring 


to. These investigators of nature who Hved in Greece from the eighth 
century onwards are only known to us through the writings of 
others, or in some cases in the form of fragments, for all their 
complete books have perished. Diels' collection of the Fragmente der 
Vorsokratiker is the most convenient source for what is left, but the 
assembling of their opinions has not been left to modern times, for 
a collection of them occurs in the writings of Plutarch of Chaeronea^ 
(3rd century a.d.). It is necessary to make use of some caution 
in describing their views, for Aristotle, as an instance, frequently 
gives the most unfair versions of the views of his predecessors. The 
account which follows is based upon Plutarch, in Philemon Holland's 
translation, and Diels. Empedocles of Akragas, who lived about 
444 B.C., believed that "the embryo derives its composition out of 
vessels that are four in number, two veins and two arteries, through 
which blood is brought to the embryo". He also held that the sinews 
are formed from a mixture of equal parts of earth and air, that 
the nails are water congealed, and that the bones are formed from 
a mixture of equal parts of water and earth. Sweat and tears, on 
the other hand, are made up of four parts of fire to one of water. 
Empedocles also had opinions about the origin of monsters and twins, 
and asserted that the influence of the maternal imagination upon the 
embryo was great so that its formation could be guided and interfered 
with. "Empedocles", says Plutarch, "saith that men begin to take 
forme after the thirtie-first day and are finished and knit in their 
parts within 50 dales wanting one. Asclepiades saith that the members 
of males because they are more hot are joynted and receive shape in 
the space of 26 dales, and many of them sooner, but are finished and 
complet in all limbes within 50 dales but females require two moneths 
ere they be fashioned, and fower before they come to their perfection, 
for that they want naturall heat. As for the parts of unreasonable 
creatures they come to their accomplishment sooner or later, ac- 
cording to the temperature of their elements." Empedocles did not 
consider that an embryo was fully alive. "Empedocles ", says Plutarch, 
"denieth it to be a creature animall, howbeit that it hath life and 
breath within the bellie, mary the first time that it hath respiration 
is at the birth, namely, when the superfluous humiditie which is in 
such unborne fruits is retired and gone, so that the aire from without 
entreth into the void vessels lying open." 

^ It is now certain that this collection is not by Plutarch himself but by an earlier 
compiler, Aetius (see Burnet). 



Anaxagoras of Clazomenae (500-428 B.C.) may have said that the 
milk of mammals corresponded to the white of the fowl's egg, but 
that observation is also attributed to Alcmaeon of Croton. It is more 
certain that he spoke of a fire inside the embryo which set the parts 
in order as it developed, and that the head was the part to be formed 
first in development. This thesis was supported by Alcmaeon, and 
by Hippon of Samos, a Pythagorean, in the fifth century B.C., but 
Diogenes of Apollonia maintained about the same time that a mass 
of flesh was formed first, and afterwards the bones and nerves were 
differentiated. Plutarch remarks about this: "Alcmaeon affirmeth 
that the head is first made as being the seat of reason. Physicians 
will have the heart to be the first, wherein the veines and arteries are. 
Some thinke the great toe is framed first, others the navill". 

The other contributions of Diogenes to this primitive embryology, 
were the view that the placenta is the organ of foetal nutrition, and 
the view that the male embryo was formed in four months but the 
female embryo not till five months had elapsed — a notion also found 
in Asclepiades and Empedocles, as we have seen. He also associated 
heat with the generation of little animals out of slime, and compared 
this with the heat of the uterus. He agreed with Empedocles that 
the embryo was not alive. "Diogenes saith that infants are bred within 
the matrice inanimate, howbeit in heat, whereupon it commeth that 
naturall heat, so soon as ever the infant is turned out of the mother's 
wombe, is drawen into the lungs." But the principal pre-Socratic 
embryologist was, as Zeller points out, Alcmaeon of Croton, who 
lived in the sixth century B.C., a disciple of Pythagoras, though ap- 
parently an independent one. He is said to have been the first man 
to make dissections. The fragments of Alcmaeon (who is not to be 
confused with Alcman, the Lacedaemonian poet) have been col- 
lected together by Wachtler; the most important are xviii and xix. 
Athenaeus in the Deipnosophists says, in his usual chatty way, "Now 
with respect to eggs Anaxagoras in his book on natural philosophy 
says that what is called the milk of the bird is the white which is in 
the eggs". This may be a wrong ascription; it may refer to Alcmaeon, 
for Aristotle says in his book on the generation of animals, "Nature 
not only places the material of the creature in the egg but also the 
nourishment sufficient for its growth, for since the mother-bird cannot 
protect the young within herself she produces the nourishment in the 
egg along with it. Whereas the nourishment which is called milk 


is produced for the young of vivipara in another part, in the breasts, 
Nature does this for birds in the egg. The opposite, however, is the 
case to what people think and what is asserted by Alcmaeoii of 
Croton. For it is not the white that is the milk, but the yolk, for it 
is this that is the nourishment of the chick, whereas they think it is 
the white because of the similarity of the colour". Whether Aristotle 
was led to this conclusion because of his erroneous ideas about the 
part played in foetal nutrition by yolk and white respectively or 
whether he recognised a similarity between yolk and milk on account 
of their fatty nature, we cannot tell. In any case, his correction of 
Alcmaeon was in the right direction, and it is interesting to compare 
the amino-acid distribution in the casein of milk and the vitellin of 
yolk, as has been done by Abderhalden & Hunter (see p. 261). 

Parmenides asserted a connection between male embryos and the 
right side of the body and between female embryos and the left side 
of the body — an idea which, considering its total lack of foundation, 
has had a very long lease of life in the world of thought. There was 
much controversy on the question of how foetal nutrition went on ; 
the atomists, Democritus (born about 460 b.c.) and Epicurus (born 
about 342 B.C.), said that the embryo ate and drank/>^r 0^. "Democritus 
and Epicurus hold", says Plutarch, "that this unperfect fruit of the 
wombe receiveth nourishment at the mouth; and thereupon it com- 
meth that so soon as ever it is borne it seeketh and nuzzeleth with the 
mouth for the brest head or nipple of the pappe : for that within the 
matrice there be certain teats; yea, and mouths too, whereby they 
may be nourished. But Alcmaeon affirmeth that the infant within 
the mother's wombe, feedeth by the whole body throughout for that 
it sucketh to it and draweth in maner of a spunge, of all the food, 
that which is good for nourishment." It would appear also that 
Democritus believed the external form of the embryo to be developed 
before the internal organs were formed. 

1-3. Hippocrates: the Beginning of Observation 

But the foregoing fragments of speculation do not really amount 
to much. The first detailed and clear-cut body of embryological 
knowledge is associated with the name of Hippocrates, of whom 
nothing certain is known save that he was born probably in the 
forty-fifth Olympiad, about 460 b.c, that he lived on the island of 
Cos in the Aegean Sea, and that he acquired greater fame as a 


physician than any of his predecessors, if we may except the legendary 
names of Aesculapius, Machaon and Podalirius. It has not been 
believed for many centuries past that all the writings in the collection 
of Hippocratic books were actually set down by him, and much 
discussion has taken place about the authenticity of individual 

Most of the embryological information is contained in a section 
which in other respects (style, etc.) shows homogeneity. We are there- 
fore rather interested in that unknown biological thinker who wrote 
the books in this class, for he could with considerable justice be 
referred to as the first embryologist. Littre discusses his identity, 
but there is no good evidence for any of the theories about it, though 
perhaps the most likely one is that he was Polybus, the son-in-law of 
Hippocrates. That the writings on generation are only slightly later 
than the time of Hippocrates is more or less clear from the fact that 
Bacchius knew of them, and actually mentions them. 

For the most part the embryological knowledge of Hippocrates is 
concerned with obstetrical and gynaecological problems. Thus in the 
Aphorisms, d(f)opicr/iioi, the books on epidemics, eirchrifxiai, the treatise 
on the nature of women, irepl rywaLKelr)'? (f)V(rio'?, the discussions of pre- 
mature birth, Trepl eirraixrjvov, the books on the diseases of women, 
irepl 'yvvaixeiaiv, and the pamphlet on superfoetation, there are many 
facts recorded about the embryo, but all with obstetrical reference. 
There are some curious notions to be found there, such as the asso- 
ciation of right and left breasts with twin embryos and a prognostic 
dependent on this. 

But the three books which are most important in the history of 
embryology are the treatise on Regimen, irepl StaLTr}<;, the work on 
generation, irepl jovr]<;, and the book about the nature of the infant, 
Trepl ^vaio<; TraiZiov. The two latter really form one continuous 
discussion, and it is not at all clear how they came to be split up 
into separate books. In the Regimen the writer expounds his funda- 
mental physiological ideas, involving the two main constituents of all 
natural bodies, fire and water. Each of these is made up of three 
primary natures, only separable in thought and never found isolated, 
heat, dryness and moisture, and each of them has the power of 
attracting, eXKeiv, their like, an important feature of the system. Life 
consists in moisture being dried up by fire and fire being wetted by 
moisture alternately, rpo^-i'i, the nourishment (moisture) coming into 


the body, is consumed by the fire so that fresh rpocfir] is in its turn 

It is important to note that the Hippocratic school was far more 
akin in its general attitude to living things to modern physiology 
than the Aristotelian and Galenic physiology. For no considerations 
of final causes complicate the causal explanations of the Hippocratic 
school, and the author of the irepl SmtV?/? indeed devotes seven chapters 
to a detailed comparison of the processes of the body {a) with the 
processes of the inorganic world both celestial and terrestrial, and 
(b) with the processes used by men in the arts and crafts, such as 
iron-workers, cobblers, carpenters and confectioners. These dis- 
cussions present distinct mechanistic features. 

He then in Section 9 sets forth his theory of the formation of the 
embryo. "Whatever may be the sex", he says, "which chance gives 
to the embryo, it is set in motion, being humid, by fire, and thus it 
extracts its nourishment from the food and breath introduced into 
the mother. First of all this attraction is the same throughout because 
the body is porous but by the motion and the fire it dries up and 
solidifies — vtto Be r?)? Kivijcno^; Koi tov irvpoii ^rfpaiveTai koI arepeovraL 
— as it solidifies, a dense outer crust is formed, and then the fire inside 
cannot any more draw in sufficient nourishment and does not expel the 
air because of the density of the surrounding surface. It therefore con- 
sumes the interior humidity. In this way parts naturally solid being up 
to a point hard and dry are not consumed to feed the fire but fortify 
and condense themselves the more the humidity disappears — these 
are called bones and nerves. The fire burns up the mixed humidity 
and forwards development towards the natural disposition of the 
body in this manner ; through the solid and dry parts it cannot make 
permanent channels but it can do so through the soft wet parts, for 
these are all nourishment to it. There is also in these parts a certain 
dryness which the fire does not consume, and they become compacted 
one to another. Therefore the most interior fire, being closed round 
on all sides, becomes the most abundant and makes the most canals 
for itself (for that was the wettest part) and this is called the belly. 
Issuing out from thence, and finding no nourishment outside, it 
makes the air pipes and those for conducting and distributing food. 
As for the enclosed fire, it makes three circulations in the body and 
what were the most humid parts become the venae cavae. In the 
intermediate part the remainder of the water contracts and hardens 


forming the flesh." In this account of the formation of the embryo, 
which seems at first sight a Httle fantastic, there are several interesting 
things to be remarked. Firstly, there is to be noted throughout it a 
remarkable attempt at causal explanations and not simply morpho- 
logical description. The Hippocratic writer is out to explain the 
development of the embryo from the very beginning on machine-like 
principles, no doubt unduly simplified, but related directly to the 
observed properties of fire and water. In this way he is the spiritual 
ancestor of Gassendi and Descartes. The second point of interest is 
that he speaks of the embryo drying up during its development, a 
piece of observation which anyone could make by comparing a 
fourth-day chick with a fourteenth-day one, and which we express 
to-day in graphical form (see Fig. 220). Thirdly, the ascription of the 
main driving force in development to fire has doubtless no direct 
relation to John Mayow's discovery, two thousand years later, that 
there is a similarity between a burning candle and a living mouse 
each in its bell-jar, and may mean as much or as little as Sir Thomas 
Browne's remark, "Life is a pure flame, and we live by an invisible 
sun within us". Yet the essential chemical aspect of living matter 
is oxidation, and the development of the embryo no less than the 
life of the adult is subject to this rule, so that what may have been 
a mere guess on the part of the Hippocratic writer, may also have 
been a flash of insight due to the simple observation which, after all, 
it was always possible to make, namely, that both fires and li\dng 
things could be easily stifled. 

Preformationism is perhaps foreshadowed in Section 26 of the 
same treatise. "Everything in the embryo is formed simultaneously. 
All the limbs separate themselves at the same time and so grow, none 
comes before or after other, but those which are naturally bigger 
appear before the smaller, without being formed earlier. Not all 
embryos form themselves in an equal time but some earlier and some 
later according to whether they meet with fire and food, some have 
everything visible in 40 days, others in 2 months, 3, or 4. They 
also become visible at variable times and show themselves to the 
light having the blend (of fire and water) which they always will 

The work on Generation is equally interesting. The earlier sections 
deal with the differences between the male and the female seed, and 
the latter is identified with the vaginal secretion. Purely embryological 


discussion begins at Section 14, where it is stated that the embryo is 
nourished by maternal blood, which flows to the foetus and there 
coagulates, forming the embryonic flesh. The proof alleged for this is 
that during pregnancy the flow of menstrual blood ceases; therefore 
it must be used up on the way out. In Section 15 the umbiHcal cord 
is recognised as the means by which foetal respiration is carried on. 
Section 1 7 contains a fine description of development with a very 
interesting analogy. "The flesh", it is said, "brought together by the 
spirit, TO TTvevfia, grows and divides itself into members, hke going to 
like, dense to dense, flabby to flabby, humid to humid. The bones 
harden, coagulated by the heat." Then a demonstration experiment 
follows : "Attach a tube to an earthen vessel, introduce through it some 
earth, sand, and lead chips, then pour in some water and blow through 
the tube. First of all, everything will be mixed up, but after a certain 
time the lead will go to the lead, the sand to the sand, and the earth 
to the earth, and if the water be allowed to dry up and the vessel 
be broken, it will be seen that this is so. In the same way seed and 
flesh articulate themselves. I shall say no more on this point". 
Here again was an attempt at causal explanation, rather than 
morphological description, in complete contrast to the later work of 


Section 22 contains a suggestive comparison between seeds of 
plants and embryos of animals, but the identification of stalk with 
umbihcal cord leads to a certain confusion. Perhaps the most inter- 
esting passage of aU is to be found in Section 29. "Now I shall speak", 
says the unknown Hippocratic embryologist, "of the characters 
which I promised above to discuss and which show as clearly as 
human intelligence can to anyone who will examine these things 
that the seed is in a membrane, that the umbilicus occupies the 
middle of it, that it alternately draws the air through itself and then 
expels it, and that the members are attached to the umbilicus. In a 
word, all the constitution of the foetus as I have described it to you, 
you will find from one end to the other if you wiU use the following 
proof Take 20 eggs or more and give them to 2 or 3 hens to incubate, 
then each day from the second onwards tiU the time of hatching, 
take out an egg, break it, and examine it. You will find everything 
as I say in so far as a bird can resemble a man. He who has not 
made these observations before will be amazed to find an umbihcus 
in a bird's egg. But these things are so, and this is what I intended 


to say about them." We see here as clearly as possible the beginnings 
of systematic embryological knowledge, and from this point onwards, 
through Aristotle, Leonardo, Harvey and von Baer, to the current 
number of the Archivf. Entwicklungsmechanik, the line runs as straight 
as Watling Street. 

In Section 30 there is an important passage in which the author 
discusses the phenomena of birth. "I say", he says, "that it is the 
lack of food which leads to birth, unless any violence has been done; 
the proof of which is this ; — the bird is formed thus from the yolk 
of the egg, the egg gets hot under the sitting hen and that which is 
inside is put into movement. Heated, that which is inside begins to 
have breath and draws by counter-attraction another cold breath 
coming from the outside air and traversing the egg, for the egg is 
soft enough to allow a sufficient quantity of respiration to penetrate 
to the contents. The bird grows inside the egg and articulates itself 
exactly like the child, as I have previously described. It comes from 
the yolk but it has its food from, and its growth in, the white. To 
convince oneself of this it is only necessary to observe it attentively. 
When there is no more food for the young one in the egg and it has 
nothing on which to live, it makes violent movements, searches for 
food, and breaks the membranes. The mother, perceiving that the 
embryo is vigorously moving, smashes the shell. This occurs after 
20 days. It is evident that this is how things happen, for when the 
mother breaks the shell there is only an insignificant quantity of 
liquid in it. All has been consumed by the foetus. In just the same 
way, when the child has grown big and the mother cannot continue 
to provide him with enough nourishment, he becomes agitated, 
breaks through the membranes and incontinently passes out into the 
external world free from any bonds. In the same way among beasts 
and savage animals birth occurs at a time fixed for each species 
without overshooting it, for necessarily in each case there must be 
a point at which intra-uterine nourishment will become inadequate. 
Those which have least food for the foetus come quickest to birth 
and vice versa. That is all that I had to say upon this subject." 

The theory underlying this passage evidently is that the main food 
of the fowl embryo is the white and that the yolk is there purely for 
constructional purposes. Had the author not been strongly attached 
to this erroneous view he could not have failed to notice the un- 
absorbed yolk-sac which still protrudes from the abdomen of the 


hatching chick, and if he had given this fact a little more prominence 
he could hardly have come to enunciate the general theory of 
birth which appears in the above passage. Moreover, had he been 
acquainted with the circulation of the maternal and foetal blood in 
viviparous animals, he could hardly have held that there was less 
food in a given amount of maternal blood at the end of development 
than at the beginning. At any rate, his attempted theory of birth 
was a worthy piece of scientific effort, and we cannot at the present 
moment be said to understand fully the principles governing incuba- 
tion time (see p. 470). 

The treatises on food and on flesh, trepl Tpo(f>rj<i and irepl aapKcovy 
are both late additions to the Hippocratic corpus, but contain points 
of embryological interest. Section 30 of the former contains some 
remarks on embryonic respiration, and Section 3 of the latter has a 
theory of formation of nerves, bones, etc. by difference of composition 
of glutinous substances, fats, water, etc. Section 6 supports the view 
that the embryo is nourished in utero by sucking blood from the 
placenta, and the proof given is that its intestine contains the 
meconium at birth. Moreover, it is argued, if this were not so, how 
could the embryo know how to suck after it is born? 

1-4. Aristotle 

After the Hippocratic writings nothing is of importance for our 
subject till Aristotle. It is true that in the Timaeus Plato deals with 
natural phenomena, eclectically adopting opinions from many pre- 
vious writers and welding them into a not very harmonious or logical 
whole. But he has hardly any observations about the development 
of the embryo. The four elements, earth, fire, air, and water, are, 
according to him, all bodies and therefore have plane surfaces which 
are composed of triangles. Applying this semi-atomistic hypothesis 
to the growth of the young animal, he says, "The frame of the entire 
creature when young has the triangles of each kind new and may 
be compared to the keel of a vessel that is just ofT the stocks ;^ they 
are locked firmly together and yet the whole mass is soft and delicate, 
being freshly formed of marrow and nurtured on milk. Now when 
the triangles out of which meats and drinks are composed come in 
from without, and are comprehended in the body, being older and 
weaker than the triangles already there, the frame of the body gets 
the better of them and its newer triangles cut them up and so the 


animal grows great, being nourished by a multitude of similar 
particles." This is as near as Plato gets to embryological speculation. 
His description has a causal ring about it, which is in some contrast 
with the predominantly teleological tone of the rest of his writings ; 
for instance, only a few pages earlier he has been speaking of the 
hair as having been arranged by God as "a shade in summer and a 
shelter in winter". It is also true that Plato may have said more 
about the embryo than appears in the dialogues. Plutarch mentions 
various speculations about sterility, and adds, "Plato directly pro- 
nounceth that the foetus is a living creature, for that it moveth and 
is fed within the bellie of the mother". 

But all this was only the slightest prelude to the work of Plato's 
pupil, Aristotle. Aristotle's main embryological book was that 
entitled Trepl ^mcov yeveaeco'i, On the Generation of Animals, but embryo- 
logical data appear in irepl ^axop, The History of Animals, irepl ^wmv 
fjLopicov, On the Parts of Animals, Trepl dva7rvofj<i, On Respiration, and 
Trepl ^Mcov Ktvrjcr€(o<i, On the Motion of Animals. All these were written 
in the last three-quarters of the fourth century B.C. 

With Aristotle, general or comparative biology came into its own. 
That almost inexhaustible profusion of living shapes which had not 
attracted the attention of the earlier Ionian and Italo-Sicilian philo- 
sophers, which had been passed over silently by Socrates and Plato, 
intent as ever upon ethical problems, but which had been for cen- 
turies the inspiration of the vase-painters and other craftsmen 
{(^coypdcjioL), was now for the first time exhaustively studied and 
reduced to some sort of order. The Hippocratic school with their 
"Coan classification of animals", which Burckhardt has discussed, 
had indeed made a beginning, but no more. It was Aristotle who 
was the first curator of the animal world, and this comparative out- 
look colours his embryology, giving it, on the whole, a morphological 
rather than a physiological character. 

The question of Aristotle's practical achievements in embryology 
is interesting, and has been discussed by Ogle. There is no doubt 
that he diligently followed the advice of the author of the Hippocratic 
treatise on generation and opened fowl's eggs at different stages 
during their development, but he learnt much more than the un- 
known Hippocratic embryologist did from them. It is also clear 
that he dissected and examined all kinds of animal embryos, mam- 
malian and cold-blooded. The uncertain point is whether he also 


dissected the human embryo. He refers in one place to an "aborted 
embryo", and as he was able to obtain easily all kinds of animal 
embryos without waiting for a case of abortion, it is likely that this 
was a human embryo. Ogle brings forward six or seven passages 
which all contain statements about human anatomy and physiology 
only to be explained on the assumption that he got his information 
from the foetus. So it is probable that his knowledge of biology was 
extended to man in this way, as would hardly have been the case if 
he had lived in later times, when the theologians of the Christian 
Church had come to very definite conclusions about the sanctity of 
foetal as well as adult life. 

The Trept i^wcov ^eveaeoo<;^ the first great compendium of embryology 
ever written, is not a very well-arranged work. There are a multitude 
of repetitions, and the order is haphazard, so that long digressions 
from the main argument are common. The work is divided into 
five books, of which the second is much the most important in the 
history of embryology, though the first has also great interest, and 
the third, fourth, and fifth contain much embryological matter mixed 
up among points of generation and sexual physiology. 

Book I begins with an introduction in which the relative significance 
of efficient and final causes is considered, and chapters i to 7 deal 
with the nature of maleness and femaleness, the nature and origin 
of semen, the manner of copulation in different animals and the 
forms of penis and testes found in them. Chapter 8 continues this, 
and describes the different forms of uterus in different animals, speaks 
of viviparity and oviparity, mentions the viviparous fishes (the 
selachians) and draws a distinction between perfect and imperfect 
eggs. Chapter 9 discusses the cetacea; 10, eggs in general; and 11 
returns to the differences between uteri. In chapter 12 the question 
is raised why all uteri are internal, and why all testes are not, and 
in chapter 13 the relations between the urinary and the genital 
systems are discussed. Copulation now receives attention again, in 
14 with regard to Crustacea, in 15 with regard to cephalopoda, and 
in 16 with regard to insecta. After this point the argument Hfts 
itself on to a more theoretical plane, and opens the question of 
pangenesis, into which it enters at length during the course of 
chapters 17 and 18, refuting eventually the widely-held view that 
the semen takes its origin from all the parts of the body so as to be 
able to reproduce in the offspring the characteristics of the parent. 


The nature of semen receives a long discussion; it is decided at last 
that it is a true secretion, and not a homogeneous natural part (a 
tissue) nor a heterogeneous natural part (an organ) nor an unnatural 
part such as a growth, nor mere nutriment, nor yet a waste product. 
It is here that the theory is put forward that the semen supplies the 
"form" to the embryo and whatever the female produces supplies 
the matter fit for shaping. The obvious question has next to be 
answered, what is it that the female supplies? Aristotle concludes 
in chapters 19 and 20 that the female does not produce any semen, 
as earlier philosophers had held, but that the menstrual blood is the 
material from which the seminal fluid, in giving to it a form, will 
cause the complete embryo to be produced. This was not a new idea, 
but had already been suggested by the author of the Hippocratic 
ire pi yovi]^. What was quite new here, was the idea that the semen 
supplied or determined nothing but the form. Chapters 21 and 22 
are rather confused ; they contain more arguments against pangenesis, 
and considerations upon the contrast between the active nature of 
the male and the passive nature of the female. Chapter 23, which 
closes the first book, compares animals to divided plants, for plants 
in Aristotle's view fertilise themselves. 

Book II opens with a magnificent chapter on the embryological 
classification of animals, showing Aristotle, the systematist, at his 
best — his classification is reproduced in Chart I. But the chapter 
also includes a brilliant discussion of epigenesis or preformation, 
fresh development or simple unfolding of pre-existent structures, 
an antithesis which Aristotle was the first to perceive, and the sub- 
sequent history of which is almost synonymous with the history of 
embryology. The question in its acutest form was not settled until 
the eighteenth century, but since then it has become clear that 
there were elements of truth in the opinion which was the less true 
of the two. Chapter 2 is not so important, though it has some 
interesting chemical analogies; it compares semen to a foam, and 
suggests that it was this foam, like that of the sea, which gave 
birth to the goddess Aphrodite^. But chapter 3 returns to the 
high level of speculation and thought found in the opening part of 
the book, for it deals with the degree of aliveness which the embryo 
has during its passage through its developmental stages. Aristotle 

^ To the Greeks all natural foams possessed a generative virtue, and a Zeus Aphrios 
was worshipped at Pherae in Thrace. 



t— I 
















T3.g u 
,« ^ I- 
.2 u:3 c« 

O O 







I— I ■ 









<U U 4J >, 

o V a -^ 

C3 C « -O 

< " ^ « cr 

^•£ u S 
«5 § o .-^ o 

L <« 


5 a, 

in O ^ 

: " " „ 

- " u " 

u o -5 o 

— ^^ ^ a 

O O iJ «J 

k ^ -S -C 

3 "^ 

? z: 

=: o 

j3 •« he 


g bo G 

'^ t: :: 

c3 c^ Ij 

r! 3 ■ — I • — 

5 C 

bo V 

s s 

u v " 

W> > rt "S bOX! h .S 





^ 'bO 

o .5 

u X! 

>< s « 

r *j o 

0-5 bo 


bO O 
bo >' 


J5 =« 



._• C ? rt 

J2 c .5 -o 

-? S m bc- 

3.^ r>< CO 

o il 

C C3 






bo bo 

C bo 







c c 

•3 ^. 







fa o< 


s -. =« o 

2 "^ "^ 



S bo 

3 2 ^ 

bci bo 


C C — 


tn rt 

2 S 

c O 





does not here anticipate the form of the recapitulation theory, but 
he certainly suggests the essence of it in perfectly clear terms. This 
chapter has also an interest for the history of theological embryology, 
for its description of the entry of the various souls into the embryo 
was afterwards made the basis for the legal rulings concerning 
abortion. This chapter also discusses embryogeny as a whole, as does 
the succeeding one. Chapter 5 is a digression into the problem 
of why fertilisation is necessary by the male, but it has also some 
curious speculations as to what extent the hen's egg is alive, if it is 
infertile. The main thread is resumed in chapters 6 and 7, two very 
fine ones, in which embryogeny and foetal nutrition are thoroughly 
dealt with, but dropped again in the last section, chapter 8, which 
is devoted to an explanation of sterility. This ends the second book. 

The third book is chiefly concerned with the application of the 
general embryological principles described in the previous book to 
the comparative field, and the fourth book contains a collection of 
minor items which Aristotle has not been able to speak of before. 

But if the work as a whole tails off in a rather unsatisfactory 
manner, its merits are such that this hardly matters. The extra- 
ordinary thing is that, building on nothing but the scraps of specula- 
tion that had been made by the Ionian philosophers, and the 
exiguous data of the Hippocratic school, Aristotle should have pro- 
duced, apparently without effort, a text-book of embryology of 
essentially the same type as Graham Kerr's or Balfour's. It is even 
very possible that Aristotle was unacquainted with any of the Coan 
school, for, though he often mentions Democritus, Anaxagoras, 
Empedocles and even Polybus, yet he never once quotes Hippo- 
crates, and this is especially odd, for Aristotle is known to have 
collected a large library. Probably Hippocrates was only known to 
Aristotle as an eminent medical man; if this is so, Aristotle's achieve- 
ments are still more wonderful. 

The depth of Aristotle's insight into the generation of animals has 
not been surpassed by any subsequent embryologist, and, con- 
sidering the width of his other interests, cannot have been equalled. 
At the same time, his achievements must not be over-estimated. 
Charles Darwin's praise of him in his letter to Ogle (which is too 
well known to quote) is not without all reservations true. There is 
something to be said for Lewes as well as Piatt. Aristotle's con- 
clusions were sometimes not warranted by the facts at his disposal, 


and some of his observations were quite incorrect. Moreover, he 
stood at the very entrance into an entirely unworked field of know- 
ledge ; he had only to examine, as it were, every animal that he could 
find, and set down the results of his work, for nobody had ever done 
it before. It was like the great days of nineteenth-century physiology, 
when, as the saying was, "a chance cut with a scalpel might reveal 
something of the first importance". 

As has already been said, Aristotle regarded the menstrual blood 
as the material out of which the embryo was made. "That, then, the 
female does not contribute semen to generation", says Aristotle, "but 
does contribute something, and that this is the matter of the cata- 
menia, or that which is analogous to it in bloodless animals, is clear 
from what has been said, and also from a general and abstract survey 
of the question. For there must needs be that which generates and 
that from which it generates, even if these be one, still they must 
be distinct in form and their essence must be different; and in those 
animals that have these powers separate in two sexes the body and 
nature of the active and passive sex also differ. If, then, the male 
stands for the effective and active, and the female, considered as 
female, for the passive, it follows that what the female would con- 
tribute to the semen of the male would not be semen but material 
for the semen to work upon. This is just what we find to be the case, 
for the catamenia have in their nature an affinity to the primitive 
matter." Thus the male dynamic element {t6 appev iroLn^TtKov) gives a 
shape to the plastic female element {to OrjXv TradrjTiKov). Aristotle 
was right to the extent that the menstrual flow is associated with 
ovulation, but as he knew nothing of the mammalian ovum, and 
indeed, as is shown in his embryological classification, expressly denied 
that there was such a thing, his main menstruation theory is wrong. 
Yet it was not an illegitimate deduction from the facts before him. 

These views of Aristotle's about the contribution of the female to 
the embryo are in striking contrast with certain conceptions of a 
century before which were probably generally held in Greece. There 
is a most interesting passage relating to them in the Eumenides of 
Aeschylus, when, during the trial scene, Apollo, defending Orestes 
from the charge of matricide, brings forward a physiological argu- 
ment. "The mother of what is called her child", Apollo is made to 
say, "is no parent of it, but nurse only of the young Hfe that is sown 
in her (jpo(f)6<; 8e Kv^iajo<i veoairopov). The parent is the male, and 


she but a stranger, a friend, who, if fate spares his plant, preserves it 
till it puts forth." 

There is evidence that this doctrine was of Egyptian origin, for 
Diodorus Siculus says, "The Egyptians hold the father alone to be 
the author of generation, and the mother only to provide a nidus 
and nourishment for the foetus". Whether this was so or not, the 
influence of such a doctrine must have been tremendous. We know 
that the conception of the female sex as playing the part of farm-land, 
i.e. of woman as a field in which grain was sown, was widespread 
in antiquity; Hartland and S. A. Cook have collected examples of 
it from Vedic, Egyptian and Talmudic sources. A late echo of it is 
to be found in Lucretius, where he refers to "Venus sowing the field 
of woman" — 

atque in eost Venus ut muliebria conserat arva. 

Nor would resemblances between mothers and children suffice to 
kill this belief, for plants may diflfer slightly according to the soil 
in which they are planted. Such an idea would be the natural 
foundation for the practice — also widespread in antiquity — of putting 
captured males to death, and retaining the females as concubines. 
On such a theory no fear would be entertained of corrupting the 
race with alien blood in this way. The whole matter affords an 
excellent illustration of the way in which an apparently academic 
theory may have the most far-reaching effects on social and political 
events, and Aristotle, far from being remote from practical affairs 
as he examined his viviparous fishes and made marginal notes on 
his copy of Empedocles, is seen to be labouring at their very root. 

The embryo, then, took its origin from the menstrual blood, on 
which, and in which, the seminal essence operated to produce it. 
But the perplexing question of the order of formation of the parts 
remained unsettled, though it had already been opened by earlier 
thinkers. What they had not done was to put the question, as it 
were, into the form of a motion ; they had not grasped the existence 
of two main alternatives, one of which would have to be chosen 
before any further progress could be made. This is just what Aristotle 
did. "There is considerable difficulty", says he, "in understanding 
how the plant is formed out of the seed or any animal out of the 
semen. Everything that comes into being or is made must (i) be 
made out of something, (2) be made by the agency of something, 


and (3) must become something. Now that out of which it is made 
is the material; this some animals have in its first form within them- 
selves, taking it from the female parent, as all those which are not 
born aHve but produced as a scolex or egg; others receive it for a 
long time from the mother by sucking, as the young of all those 
which are not only externally but also internally viviparous. Such 
is the material out of which things come into being, but we now 
are enquiring not out of what the parts of an animal are made, but 
by what agency. Either it is something external which makes them 
or else it is something existing in the seminal fluid and the semen; 
and this must either be soul or a part of a soul, or something con- 
taining soul." Aristotle concludes that there is no external shaping 
influence, but only something or other contained in the embryo itself. 
To this extent he was wrong, for the influence of the proper physico- 
chemical environment on the growing embryo is as important as its 
physico-chemical internal constitution (later he modified his views 
on this). But now he goes on to deal with the main question, and 
says, "How then does it (the shaping influence) make the other parts? 
All the parts, as heart, lung, liver, eye, and all the rest, come into 
being either together or in succession, as is said in the verse ascribed 
to Orpheus, for there he says that an animal comes into being in 
the same way as the knitting of a net. That the former is not the 
fact is plain even to the senses, for some of the parts are clearly 
visible as already existing in the embryo wliile others are not; that 
it is not because of their being too smaU that they are not visible is 
clear, for the lung is of greater size than the heart, and yet appears 
later than the heart in the original development". This passage 
demonstrates that Aristotle had opened hen's eggs at different stages, 
and was well acquainted with the appearances presented there as 
early as the third day. He goes on to set forth a further alternative. 
Agreeing that a continuously new formation of parts takes place, and 
not merely an unfolding of parts already present in the semen or the 
menstrual blood, is this brought about by a chain of creations or by 
one original creation? In other words, does the heart come into being 
first, and then proceed to form the liver, and then the liver go on 
to form the lungs, or do they simply appear one after the other without 
such a creative inter-relationship? Aristotle argues against the former 
view on the ground that if one organ formed another, the second 
one would have to resemble the first in some way, which is not the 



case. His words on this subject cannot be condensed. "But neither 
can the (formative) agent be external and yet it must needs be one 
or other of the two. We must try then to solve this difficulty, for 
perhaps some one of the statements made (already) cannot be made 
without qualification, e.g. the statement that the parts cannot be 
made by what is external to the semen. For if in a certain sense they 
cannot, yet in another sense they can." (Thus Aristotle does some 
justice to the environment.) "It is possible, then, that A should 
miove B and B should move C, that, in fact, the case should be the 
same as with the automatic machines shown as curiosities. For the 
parts of such machines while at rest have a sort of potentiality of 
motion in them, and when any external force puts the first of them 
into motion, immediately the next is moved in actuality. As, then, 
in these automatic machines the external force moves the parts in 
a certain sense (not by touching any part at the moment but by 
having touched one previously) , in like manner also that from which 
the semen comes or in other words that which made the semen, sets 
up the movement in the embryo and makes the parts of it by having 
touched first something though not continuing to touch it. In a way 
it is the innate motion that does this, as the act of building builds 
a house. Plainly, then, while there is something which makes the 
parts, this does not exist as a definite object, nor does it exist in the 
semen at the first as a complete part." This notion of the setting 
in motion of a wound-up clock is substantially modern and underlies 
the physico-chemical analysis of the developing embryo. It is really 
striking to find Aristotle using the machine analogy in order to explain 
himself, for he, of all biologists, emphasised the final cause in natural 
operations. However, he soon returns to a more vitalistic attitude 
in the succeeding section. "But how is each part formed?" he says. 
"We must answer this by starting in the first instance from the 
principle that, in all products of Nature or art, a thing is made by 
something actually existing out of that which is potentially the same 
as the finished product. Now the semen is of such a nature and has 
in it such a principle of motion, that when the motion is ceasing 
each of the parts comes into being and that as a part having life or 
soul. . . .And just as we should not say that an axe or other instrument 
or organ was made by the fire alone, so neither shall we say that foot 
or hand were made by fire alone . . . .While, then, we may allow that 
hardness and softness, stickiness and brittleness, and whatever other 


qualities are found in the parts that have life and soul, may be caused 
by mere heat and cold yet, when we come to the principle, Xoyof, 
in virtue of which flesh is flesh and bone is bone, that is no longer so ; 
what makes them is the movement set up by the male parent, who 
is in actuality what that out of which the offspring is made is in 
potentiaUty . This is what we find in the products of art ; heat and 
cold may make the iron soft or hard, but what makes a sword is the 
movement of the tools employed, this movement containing the 
principle of the art. For the art is the starting-point and form of 
the product; only it exists in something else (i.e. potentially in the 
mind of the artist), whereas the movement of nature exists in the 
product itself, issuing from another Nature (i.e. the parent) which 
has the form in actuaHty." 

Thus Aristotle, evidently influenced by his doctrine of "form" and 
"matter", decided against preformation and pictured at one and 
the same time the unformed catamenia as containing a kind of clock- 
work m.echanism which, once set in motion, would inevitably produce 
the finished embryo, and also as an inchoate substance on which 
the seminal essence should act like a swordmaker producing a sword 
according to the motions of a natural art. These two ideas are not 
completely reconciled in Aristotle, and a consideration of artificial 
fertiHsation would have provided a test case, had he been able to 
know of the experiments of Delage and Loeb. For, on his second 
theory, butyric acid would transmute a sea-urchin's egg into butyric 
acid and not into a sea-urchin: while, on his first theory, the egg 
would make the sea-urchin irrespective of what influence it was that 
swung the starting-handle. 

Aristotle has a good deal to say about the theory of recapitulation, 
as it was afterwards to be called. He thought there was no doubt 
that the vegetative or nutritive soul existed in the unfertilised material 
of the embryo, "for nobody", as he says, "would put down the un- 
fertilised embryo as soulless or in every sense bereft of life (since 
both the semen and the embryo of an animal have every bit as 
much life as a plant) and it is productive up to a certain point. ... As 
it develops it also acquires the sensitive soul in virtue of which an 
animal is an animal. . . . For first of all such embryos seem to live 
the life of a plant, and it is clear that we must be guided by this in 
speaking of the sensitive and the rational soul. For all three kinds 
of soul, not only the nutritive, must be possessed potentially before 


they are possessed actually". These passages show very clearly the 
line of thought contained in the recapitulation theory, as do the 
following. "For an animal does not become at the same time an 
animal and a man or a horse or any other particular animal", i.e. 
the more general appears first and the more particular later. "For 
the end is developed last, and the peculiar character of the species 
is the end of the generation in each individual", i.e. the embryo 
attains the point of being definitely not a plant before it attains that 
of being definitely not a mollusc but a horse or a man. Aristotle 
concludes that the diflferent sorts of souls enter the embryo at different 
stages of development, just as the shape of the embryo gradually 
approximates to whatever adult shape it is destined to conform to. 

Aristotle continues to discuss the central problems of embryology, 
but now in a way which presents features of directly physico-chemical 
interest. "When the material secreted by the female in the uterus 
has been fixed by the semen of the male (this acts in the same way 
as rennet acts upon milk, for rennet is a kind of milk containing vital 
heat, which brings into one mass and fixes the similar material, and 
the relation of the semen to the catamenia is the same, milk and the 
catamenia being of the same nature) , when, I say, the more solid 
part comes together, the liquid is separated off from it, and as the 
earthy parts solidify, membranes form all round it; this is both a 
necessary result and for a final cause, the former because the surface 
of the mass must solidify on heating as well as on cooling, the latter 
because the foetus must not be in a liquid but separated from it." 
Later on, he also says, "The reason is similar to that of the growth 
of yeast, for yeast also grows great from a small beginning as the more 
sohd part liquefies and the liquid is aerated. This is effected in 
animals by the nature of the vital heat, in yeasts by the heat of the 
juice contained in them". 

These remarkable passages contain the first reference to enzyme 
action ever made in a discussion on embryology. The solidification of 
the outer crust is of course Hippocratic, as we have already seen. The 
part about the amnios is unfortunate ; for the facts are exactly contrary. 

"The heart is first differentiated", says Aristotle, "as is clear not 
only to the senses (for it is so) but on theoretical grounds. For when- 
ever the young animal has been separated from both parents it must 
be able to manage itself, like a son who has set up house away from 
his father." This is good observation. "The heart is the principle 


and origin of the embryo", says Aristotle. This conception of cor 
primum vivens, ultimum moriens (a phrase never used by Aristotle 
himself), has henceforward a long and tortuous history, which has 
been described by Ebstein and others. 

Aristotle goes on to describe the membranes of the mammalian 
foetus with its umbilical cord: "The vessels join on to the uterus 
like the roots of plants and through them the embryo receives its 
nourishment. This is why the embryo remains in the uterus"; not 
as Democritus thought, so that it might be moulded into the maternal 
shape. The embryo "straightway sends off the cord like a root to 
the uterus ". He carefully notes, as if the conception of axial gradients 
was existing deep down in his mind, that the cephalic parts of the 
embryo are formed first. "The greater become visible before the less ", 
he says, "even if some of them do not come into being before them. 
First the parts above the hypozoma" (a term more or less corre- 
sponding to "diaphragm") "are differentiated and are superior in 
size, the part below is both smaller and less differentiated. This 
happens in all animals in which exists the distinction of upper and 
lower, except in the insects." Aristotle gives as his explanation of 
this a teleological argument: "This is why the parts about the head 
and especially the eyes appear largest in the embryo at an early 
stage, while the parts below the umbilicus, as the legs, are small; 
for the lower parts are for the sake of the upper and are neither 
parts of the end, nor able to form it". 

Embryonic growth is thus described by Aristotle: "The homo- 
geneous parts (tissues) are formed by heat and cold, for some are 
put together and solidified by the one and some by the other .... 
The nutriment oozes through the blood-vessels and the passages in 
each of the parts, like water in unbaked pottery, and thus is formed 
the flesh or its analogues, being solidified by cold, which is why it 
is dissolved by fire. But all the particles given ofT which are too 
earthy, having but little moisture and heat, cool as the moisture 
evaporates along with the heat, so they become hard and earthy in 
character, as nails, horns, hoofs, and beaks, and therefore they are 
softened by fire but none of them is melted by it, while some of them, 
as egg-shells, are soluble in liquids. The sinews and bones are formed 
by the internal heat as the moisture dries, and hence the bones are 
insoluble by fire like pottery, for like it they have been as it were 
baked in an oven by the heat in the process of development. . . . The 


skin, again, is formed by the drying of the flesh, Hke the scum upon 
boiled substances; it is so formed not only because it is upon the 
outside, but also because what is glutinous, being unable to evaporate, 
remains on the surface". Here is a splendid collection of mechanical 
processes, but Aristotle is careful to add: "As we said, all these things 
must be understood to be formed in one sense of Necessity, but in 
another sense not of Necessity but for a Final Cause". 

Concurrent growth and differentiation, the former being temporally 
sequent to the latter, he thus describes: "The upper half of the body, 
then, is first marked out in the order of development ; as time goes 
on the lower also reaches its full size in the sanguinea. All the parts 
are first marked out in their outlines and acquire later on their colour 
and softness or hardness, exactly as if Nature were a painter producing 
a work of art, for painters too first sketch in the animal with lines 
and only after that put in the colours". Aristotle had some difficulty 
about the eyes; he noted that they were disproportionately large 
in early bird embryos, but he seems to have thought that they shrunk 
absolutely as well as relatively during further development. It takes 
him a great deal of ingenuity to invent a teleological explanation for 
this quite imaginary fact. 

The food which the embryo derives from the mother, according 
to Aristotle, is of two distinct kinds, nutritious, formative, or creative, 
TO OpeTTTLKov, and that which is concerned with simple increase of 
size, TO et? fxeyedo'; itolovv tijv eirihoaiv. This distinction is difficult to 
understand, and, though it would be attractive to interpret the former 
as vitamines and the latter as fats, proteins and carbohydrates, that 
would probably be putting too much of a strain on our belief in 
Aristotle's insight. He has much to say of the placenta, and ascribes 
to it its correct function. He combats the idea that foetal nutrition 
is maintained by uterine paps, alleging against it the fact that all 
embryos are enclosed in membranes. He discusses birds' eggs in 
great detail, referring to infertile or "wind-eggs" and to the action 
of heat during incubation. He considered that the embryo was 
formed from the white exclusively, and only got its nourishment 
from the yolk, which was a backward step in view of what had already 
been said by the Hippocratic embryologist. He knew of the whiteness 
of the yolk when first formed in the oviduct and of the yellow colour 
of the layers of yolk added to it in its passage down that tube, but 
he held that the yellow colour was "sanguineous", and therefore hot, 


while the white was cold. He held also that the bird embryo always 
developed at the pointed end; no doubt, as Piatt has suggested, 
Aristotle belonged to Swift's class of "Little-endians", and must have 
always opened them at that end, in which case he would find the 
embryo there, for the yolk always swims embryo uppermost. He 
knew also that the yolk liquefied during the first week of develop- 
ment, and that it grew larger, but he did not guess the right reasons 
of these phenomena. He knew the arrangements for embryonic 
development in the dolphins and ovo viviparous sharks. He takes 
a strong line over spontaneous generation; "nothing", he says, 
"comes into being by putrefying, but by concocting". And so in 
many other passages where detailed observation is joined with acute 
reasoning. So far only the treatise on the generation of animals 
has been under consideration. But in the irepl ^oiwv, also, there are 
many embryological data, and it is strange that those detailed 
observations upon the developing fowl embryo, which demonstrate 
more than anything else Aristotle's wonderful powers of observation, 
are not contained at all in the Generation of Animals, but in the History 
of Animals. He takes animals one by one in order, and in each case 
deals with their generative peculiarities, such as their mode of 
hatching, their incubation period, their fertility, etc. For instance, 
he correctly relates how cartilaginous fish embryos possess a yolk-sac 
like bird embryos, but no allantois. In his account of the fowl he is 
unusually precise. 

Most of the sixth book is occupied with the account of the genera- 
tion of birds and fishes, and the seventh treats also very fully of that 
of man. But in both cases it is a description that is given; more 
theoretical considerations are left to the book on generation, and for 
this reason the latter work is the more interesting. From a general 
point of view the History of Animals has a more wonderful wealth 
of material in it than the book on generation, but, at the same time, 
it also indulges in much more extravagant stories, such as those of 
the "kindly and gentle dolphin" and the equine Oedipus, and to 
that extent the austerity of the book on generation charms us more. 

Other treatises also mention embryology. The irepl ^(owv fioployvj On 
the Parts of Animals, has a passage in which the appearance of the 
third-day chick embryo is described, and refers to observations on 
the lack of pigment and of distinct medullary canals in bones in 
foetal life. The small work entitled Trepl dvairvoTj^;, On Respiration, also 


refers to the heart as the first organ to be formed, and so as the seat 
of the soul. But these minor sources contribute little to the progress 
of the science, and it is upon the great work On the Generation of Animals 
that Aristotle's well-deserved fame as an embryologist will always rest. 

If I have devoted a very large space to an account of Aristotle's 
contributions to embryology, it is, firstly, because they are actually 
greater in number than those of any other individual embryologist, 
and secondly, because they had so profound an influence upon the 
following twenty centuries. Embryology from the third century B.C. 
to the seventeenth century a.d. is meaningless unless it is studied in 
the light of Aristotle. 

His outstanding contributions to embryology may be put in the 
following way: 

1. He carried to their logical conclusion the principles of the 
observation of facts suggested by the unknown Hippocratic 
embryologist, and added to them a discipline of classification 
and correlation of facts which gave embryology a quite new 

2. He introduced the comparative method into embryology, and 
by studying a multitude of living forms was able to lay the 
foundation for future science of the various ways in which 
embryonic growth can take place. Thus he knew of oviparity, 
ovoviviparity, and viviparity, and one of his distinctions is 
substantially the same as that known to modern embryology 
between holoblastic and meroblastic yolks. 

3 . He distinguished between primary and secondary sexual charac- 

4. He pushed back the origin of sex-determination to the very 
beginning of embryonic development. 

5. He associated regeneration phenomena with the embryonic 

6. He reaUsed that the previous speculations on the formation of 
the embryo could be absorbed into the definite antithesis of pre- 
formation and epigenesis, and he decided that the latter alterna- 
tive was the true one. 

7. He put forward a conception of the unfertilised egg as a com- 
plicated machine, the wheels of which would move and 
perform their appointed function in due course when once the 
master-lever had been released. 


8. He foreshadowed the theory of recapitulation in his specula- 
tions on the order in which the souls came to inhabit the 
embryo during its growth, and in his observation that 
universal characteristics precede particular characteristics in 

9. He foreshadowed the theory of axial gradients by his observa- 
tions on the greater and more rapid development of the cephalic 
end in the embryo. 

10. He allotted the correct functions to the placenta and the 
umbilical cord. 

11. He gave a description of embryonic development involv- 
ing comparison with the action of rennet and yeast, fore- 
shadowing thus our knowledge of organic catalysts in 

But there was another side to the picture. Aristotle made three 
big mistakes, and here I do not refer to any matters of detail, in 
which it would not have been humanly possible to be more than 
very often right, but rather to general notions, such as the eleven 
correct ones. 

They were as follows : 

1. He was incorrect in his view that the male supplies nothing 
tangible to the female in the process of fertilisation. To say 
that the semen gave the "form" to the inchoate "matter" of 
the menstrual blood was equivalent to saying that the seminal 
fluid carried nothing in it but simply an immaterial breath 
along with it. Aristotle did not envisage the existence of 

2. He was entirely wrong in his teaching about the scolex. The 
caterpillar is not, as he supposed, an egg laid too soon, but has 
already passed through the embryonic state. 

3. He was misled by some observations on castrated animals and 
so did not ascribe to the testis its true function. 

Such mistakes as these, however, were not nearly so important as 
the solid ground gained by his correct answers. They were always 
open to experimental test, even though the authority of his name 
precluded it until the Renaissance. But there was one aspect 
of his embryological work which was to exercise an unfortunate 
influence on the subsequent progress of the science, namely, his in- 
sistence on teleological explanations. He was always seeking for 


final as well as efficient causes. "The ancient Nature-philosophers 
did not see that the causes were numerous ; they only saw the material 
and efficient causes and did not distinguish even these, while they made 
no enquiry at all into the formal and final causes." "Democritus", 
he says, "neglecting the final cause, reduces to Necessity all the 
operations of Nature. Now they are necessary it is true, but yet 
they are also for a final cause, and for the sake of what is best in 
each case." 

Now in Aristotle this was all to the good. A metaphysician as well 
as a scientific worker, he was able to use the concept of purposiveness 
as a heuristic aid, but he never rested upon it. The trouble was 
that he introduced it into the discussion at all. It is an interesting 
speculation to consider what would have happened if the first great 
biologist had not brought final causes into his teaching ; perhaps the 
subsequent history of biology, and science as a whole, would have 
been very different. For final causes irresistibly led to the theological 
blank alleys into which men's thoughts were ushered and there left 
to grope till the end of the Middle Ages. 

Perhaps Aristotle would not have made so many great discoveries 
if he had been more of a Democritus. For teleology is, like other 
varieties of common sense, useful from time to time; e.g. Harvey told 
Boyle that he was led to certain important considerations by meditat- 
ing upon the final cause of the valves in the veins ; and every biologist 
acts in the same way at the present time. But the important thing 
is not to give the last word to teleology. And those attractive shady 
places which Aristotle, guided by his genius, quickly passed through 
on his perpetual journeys into the hot sunlight of research and specu- 
lation were so many traps for those who followed him. He himself 
knew how to change rapidly from metaphysician into physicist and 
back again, how to bow politely to the final cause and press on with 
the dissection; but the later Peripatetics had no knowledge of this art, 
nor had the Patristic Doctors, nor the mediaeval Aristotelians; who 
all remained sleeping quietly in the shade of the will of God. He knew 
very well from the sea (to use Bacon's metaphor at last) the look of 
the Circe country of teleology, but he never visited it for long at a 
time^ being an authentic Odysseus, unlike so many later heads, who, 
following the example of Plato, "anchored upon that shore" and, 
dropping their hooks to the sound of plain-song, there rode, never 
to hoist sail again. 


1-5. The Hellenistic Age 

Aristotle died in 322 e.g. From that year until 1534, the date of 
the birth of Volcher Goiter, first in time of the Renaissance embryo- 
logists, embryology has very little history. 

The founder of the stoical philosophy, Zeno of Gitium, was born 
some twenty years before the death of Aristotle. "Pious and mag- 
nanimous as Stoicism was in the field of conduct", says AUbutt, 
"creating or nourishing that elevation of mind which distinguished 
the nobler Roman of the Empire, yet in Rome, as in England, its 
natural science was of no account. The spirit of it was indeed rather 
alien than akin to science. The mind of the Porch which called itself 
'practical' was reluctant to all 'speculation', natural science in- 
cluded." The Stoics regarded the four quahties of cold, hot, wet, 
and dry, as ultimate, instead of the earth, fire, air, and water of the 
Peripatetics and their predecessors, Plutarch, in his summary of 
philosophic opinions already mentioned, has some passages relating 
to their views on the development of the embryo. "The Stoicks say", 
he relates, "that the foetus is fed by the fecundine and navell; where- 
upon it is that midwives presently knit up and tie the navell string 
fast, but open the infants mouth, to the end that it be acquainted 
with another kind of nourishment." And elsewhere, "The Stoicks 
say that it is a part of the wombe and not an animall by itselfe. For 
like as fruits be parts of trees, which when they be ripe do fall, even 
so it is with an infant in the mother's wombe. . . . The Stoicks are 
of opinion that the most parts are formed all at once ; but Aristotle 
saith the backbone and loines are first framed like as the keele in 
a ship." But to which of Zeno's successors, Gleanthes, Ghrysippus, 
Grates or the rest, these sayings are to be attributed, is not known. 

The Epicureans also had opinions on these subjects. They thought 
that the foetus in utero was fed by the amniotic liquid or the blood, 
and they also beheved, in contradistinction to the Peripatetics, that 
both male and female supplied seed in generation, as is shown by 
the lines of Lucretius : 

usque adeo magni refert, ut semina possint 
seminibus commisceri genitaliter apta 
crassaque conveniant liquidis at liquida crasso. 

But much more important than the teaching of these philosophers 
was the rise of what might be called the scientific faculty of the great 


University of Alexandria. That seat of learning, perhaps the most 
glorious, after Athens, of any in antiquity, and greater than its con- 
temporary rival Pergamos, was important because all the traditions 
of earlier times were united in it like a bundle of strands coming 
together to form a rope. Democritean atomism. Peripatetic science 
and metaphysics, Goan biology, Coan and Cnidian medicine, above 
all, Athenian mathematics and astronomy, all were gathered in 
the fMovaelov of Alexandria under the benevolent dynasty of the 
Ptolemies. The link between the Alexandrian biologists and the 
school of Aristotle was Straton of Lampsacus, who, though apparently 
not making any contribution to embryology himself, must have 
brought the knowledge of generation gained by Aristotle to Alex- 
andria as he sailed south across the Mediterranean to be the tutor 
of Ptolemy Philadelphus. The link between Cos and Alexandria was 
Diodes of Carystus, who was the last of the Hippocratic school and 
also a pupil of Philistion of Locri. Diodes has a certain importance 
in the history of embryology; for Oribasius refers to him as the dis- 
coverer of the punctum saliens in the mammalian embryo, "on the 
ninth day a few points of blood, on the eighteenth beating of the 
heart, on the twenty-seventh traces of the spinal cord and head ". He 
thus showed that the early development of chick and mammal was 
very alike. Plutarch also tells us that he occupied himself with the 
question of sterility. He described the human placenta, as well as 
embryos of twenty-seven and forty days, and he held that both male 
and female contribute seed in generation. Cnidian medicine in- 
fluenced Alexandria through Chrysippus of Cnidus — not the Stoic — 
whose embryological doctrine seems to have been that the embryo had 
only a vegetative soul until birth or hatching. 

All these influences were fruitful, for they produced the two 
greatest physiologists of ancient times, Herophilus of Chalcedon and 
Erasistratus of Chios. These two, who were contemporaries during 
the third century B.C., experimented much and wrote voluminously, 
but all except fragments of their writings have been lost, and can 
now only be pieced together out of the books of Galen, as has been 
done by Dobson. Allbutt has well described the differences between 
them, such as the predilection of Herophilus for the humoral patho- 
logy and pharmacy, and the greater interest taken by Erasistratus in 
atomistic speculations. "Herophilus", says Plutarch, "leaveth to 
unbome babes a mooving naturall, but not a respiration, of which 


Co[N-re-MPoR.A(e.r EveNfrs and 


motion the sinewes be the instrumental! cause, but afterwards they 
become perfect Hving animall creatures, when being come forth of 
the wombe, they take in breath from the aire." 

Herophilus described the ovaries and the Fallopian tubes, but did 
not advance further than Aristotle towards correct sexual physiology 
in this respect. We gather that he made many dissections of embryos 
from the testimony of Tertullian, though this may not be worth much. 
Moreover, he called the outer membrane of the brain, chorion, after 
the membranes which surround the embryo. He gave a correct de- 
scription of the umbilical cord, except that he assigned to it four vessels 
instead of three, carrying blood and breath to the embryo. The 
veins, he thought, communicated with the venae cavae, and the 
arteries with the great artery running along the spine. Herophilus 
also occupied himself much with obstetrical matters, and wrote a 
treatise on them, fiaicoTtKov. Together with Erasistratus he denied 
that there were any diseases special to women other than those 
attendant on their special sexual functions, but the greatest contribu- 
tion which he made to biology was the association of the brain with 
the intellect^, for even Aristotle had made the he^rt the seat of the 
mental individual. 

Erasistratus did not study embryology as much as did Herophilus, 
but a passage in Galen throws an interesting light on his notions of 
embryonic growth. "The heart", says Galen, "is no larger at first 
than a millet seed, or, if you like, a bean. Ask yourself how it could 
grow large otherwise than by being distended and receiving nutri- 
ment throughout its whole extent, just as we have shown above that 
the seed is nourished. But even this is unknown to Erasistratus, who 
makes so much of Nature's Art. He supposes that animals grow just 
like a sieve, a rope, a bag, or a basket, each of which grows by the 
addition to it of materials similar to those out of which it began to 
be made." This is only one instance out of many in which Galen, the 
teleologist, finds fault with Erasistratus, the mechanistic philosopher. 

During the period when the biological school of Alexandria was 
at its height, that city became an important Jewish centre. Two 
centuries later it was to produce Philo, but now the Alexandrian 
Jews were writing that part of the modern Bible known as the Wisdom 
Literature. In books such as the Wisdom of Solomon, Ecclesiasticus, 
Proverbs, etc., the typical Hellenic exclusion of the action of gods 

^ This was not absolutely new: Alcmaeon had held the same view (see Burnet). 


in natural phenomena is clearly to be seen. There are two passages 
of embryological importance. Firstly, in the book of Job (x, 9-1 1), 
Job is made to say, "Remember, I beseech thee, that thou hast 
fashioned me as clay; and wilt thou bring me into dust again? 
Hast thou not poured me out as milk, and curdled me like cheese? 
Thou hast clothed me with skin and flesh, and knit me together with 
bones and sinews". This comparison of embryogeny with the making 
of cheese is interesting in view of the fact that precisely the same 
comparison occurs in Aristotle's book On the Generation of Animals, as 
we have already seen. Still more extraordinary, the only other 
embryological reference in the Wisdom Literature, which occurs in 
the Wisdom of Solomon (vii, 2), also copies an Aristotelian theory, 
namely, that the embryo is formed from (menstrual) blood. There 
the speaker says, "In the womb of a mother was I moulded into 
flesh in the time of ten months, being compacted in blood of the 
seed of man and the pleasure that came with sleep". Perhaps 
it is no coincidence that both these citations can be referred back 
to Aristotle, and, in the second case, even to Hippocrates; perhaps 
the Alexandrian Jews of the third century B.C. were studying Aristotle 
as attentively as Philo Judaeus studied Plato a couple of hundred 
years later. 

The Alexandrian school was directly responsible for the introduc- 
tion of Greek medicine and biology into Rome, through the physician 
Cleophantus, who seems to have been particularly interested in 
gynaecology. At the end of the second century B.C. and the beginning 
of the first, Rome received the first and greatest of her Greek 
physicians, Asclepiades of Parion, who brought atomism with him. 
He was thus the Hnk between Epicurus and the methodistic school 
of physicians, and may have been a potent influence upon Lucretius. 
Again, Alexander Philalethes provides the link between Cleophantus 
and Soranus. Soranus lived in Rome from about a.d. 30 tifl just 
after the end of the first century, and so twenty years before the 
birth of Galen. 

Of aU the ancient writers on embryology, Soranus is the one whose 
works were in later times most widely appropriated, mutilated, 
furbished up, quoted from rightly and wrongly, and generally upset. 
Allbutt, Barbour and Singer give accounts of the way in which this 
process went on, and the whole question has given rise to a con- 
siderable literature. (See Lachs, Ilberg, Sudhov, etc.) It lasted 


right into the Middle Ages, and was particularly vehement in the 
case of the treatise on gynaecology, Trepl ywaiKeLwv Tradotv. This was 
translated into Latin under the name of Moschion, then back into 
Greek and finally back into Latin again. It is largely obstetrical, 
but it shows an advanced knowledge of embryology, and especially 
an accurate idea of the anatomy of the uterus. (See Plate II.) 

The other writers of this period are unimportant embryologically. 
Among the Greeks, Aelian wrote a De natura animalium, in which 
he spoke of eggs, but without adding anything to our knowledge of 
them; Nicander in his Theriaca refers to mammalian embryos, and 
alleges that they breathe and eat through the umbilical cord; and 
Oppian has a few unsystematic remarks about the embryos of various 
animals. Junius Columella's work on husbandry contains two chapters 
on eggs, but he was not much interested in the theoretical aspect of 
development. In Aulus Gellius we have the cheese analogy appearing 
in conjunction with obscurantist views about the powers of the number 
seven. It is not generally known that a clear statement of the pre- 
formationist or " Entfaltung " theory of embryogeny occurs in Seneca's 
Quaestiones naturales, where there is the following passage: "In the 
seed are enclosed all the parts of the body of the man that shall be 
formed. The infant that is borne in his mother's wombe hath the 
rootes of the beard and hair that he shall weare one day. In this 
little masse likewise are all the lineaments of the bodie and all that 
which Posterity shall discover in him". Perhaps this notion was 
derived by Seneca from the Homoeomereity of Anaxagoras, for a 
discussion of which in relation to embryology, see Cornford. "Hair 
cannot come out of not-hair, nor flesh out of not-flesh", said 

The Natural History of Pliny, that "voluminous, industrious, un- 
philosophical, gullible, unsystematic old gossip", as Singer justly 
calls him, contains little of embryological importance, although he 
devotes many sections to eggs, and what there is comes straight from 
the fountain-head, Aristotle. As, for example, "All egs have within 
them in the mids of the yolk, a certain drop, as it were of bloud, 
which some thinke to be the heart of the chicken, imagining that, 
to be the first that in everie bodie is formed and made ; and certainlie 
a man shall see it within the verie cggc to pant and leape. As for 
the chick, it taketh the corporall substance, and the bodie of it is 
made of the white waterish liquor in the egge, the yellow yolke 


'■ jj.V^ki^-vfc . i ^ imj^oi^^ 

!^ Lfe<? l^i n 1^ tm 

J. J O € ^4 

^ t ;:: t o^^fi " 




serves for nourishment; whiles the chick is unhatched and within the 
egge, the head is bigger than all the bodie besides; and the eies 
that be compact and thrust together be more than the verie head. 
As the chick within growes bigger, the white turneth into the middest, 
and is enclosed within the yolke. By the 20 day (if the eggs be stirred) 
ye shall heare the chick to peepe within the verie shell; from that 
time forward it beginneth to plume and gather feathers ; and in this 
manner it lies within the shell, the head resting on the right foot, 
and the same head under the right wing, and so the yolke by little 
and little decreaseth and faileth". But the best way to illustrate 
Pliny's embryology is to copy out some of his index, as follows : 

The Table to the first Tome of Plinies Naturall Historie. 

Egs diverse in colour 298 

Egs of birds of 2 colours within the shell ibid. 

Egs of fishes of i colour ibid. 

Egs of birds, serpents, and fishes, how they differ ibid. 

Egs best for an hen to sit upon 299 

Egs hatched without a bird, onely by a kind heat ibid. 

Egs how they be marred under an hen ibid, 

wind-egs, called Hypenemia 300 

how they be engendred 301 

wind-egs, Zephyria ibid. 

Egs drawne through a ring ibid. 

Egs how they be best kept ibid. 

The Table to the second Tome of Plinies Naturall Historie, 

Egs of hens and their medicinable properties 351 

yolke of hens egs, in what cases it is medicinable 352 

Egs all yolke, and without white, be called Schista ibid, 

skinne of an Hens egge-shell, good in Physicke ibid. 

Hens Eggeshell reduced unto ashes, for what it serveth ibid, 

the wonderfull nature of Hens Eggeshels ibid. 

Hens Egges, all whole as they be, what they are good for 353 

the commendations of Hens Egges, as a meat most medicinable ibid. 
Hens Egge, a proper nourishment for sicke folks, and may go 

for meat and drinke both ibid. 

Egge-shels, how they may be made tender and pliable ibid, 

white of an Egge resisteth fire ibid, 

of Geese Egges a discourse 354 
the serpents egge, which the Latines call Anguinum, what it 

is, and how engendred 355 

This last item exhibits Pliny at his worst. It is worth quoting, apart 
from its intrinsic value, for it shows to what depths embryological 
knowledge descended within four hundred years after Aristotle col- 
lected his specimens on the shores of the lagoon of Pyrrha, and talked 
with the fishermen of Mitylene. "I will not overpasse one kind of 
eggs besides, which is in great name and request in France, and 
whereof the Greeke authors have not written a word ; and this is 



the serpents egg, which the Latins call Anguinum. For in Summer 
time yerely, you shall see an infinit number of snakes gather round 
together into an heape, entangled and enwrapped one within another 
so artificially, as I am not able to expresse the manner thereof; by 
the means therefore, of the froth or salivation which they yeeld from 
their mouths, and the humour that commeth from their bodies, 
there is engendred the egg aforesaid. The priests of France, called 
Druidae^, are of opinion, and so they deliver it, that these serpents 
when they have thus engendred this egg do cast it up on high into 
the aire by the force of their hissing, which being observed, there 
must be one ready to catch and receive it in the fall again (before 
it touch the ground) within the lappet of a coat of arms or souldiours 
cassocks. They affirme also that the party who carrieth this egg away, 
had need to be wel mounted upon a good horse and to ride away 
upon the spur, for that the foresaid serpents will pursue him still, 
and never give over until they meet with some great river betweene 
him and them, that may cut off and intercept their chace. They ad 
moreover and say that the only marke to know this egg whether it 
be right or no, is this, that it will swim aloft above the water even 
against the stream, yea though it were bound and enchased with a 
plate of gold." But one must not be too severe upon Pliny, for he 
and his translator, Philemon Holland, provide an entertainment 
unequalled anywhere else. 

To some extent the same applies to Plutarch of Chaeronea, who 
lived about the same time. Plutarch's writings, inspired as they were 
throughout by the desire to commend the ancient religion of Greece 
to a degenerate age, represent no milestone or turning-point in the 
history of embryology, yet there is a passage in the Symposiaques, or 
Table-questions which bears upon it. The third question of book 2 
is "Whether was before, the hen or egg?" "This long time", says 
Plutarch, "I absteined from eating egges, by reason of a certaine 
dream I had, and the companie conceived an opinion or suspition 
of me that there were entred into my head the fantasies and super- 
stitions of Orpheus or Pythagoras, and that I abhorred to eat an 
egge for that I believed it to be the principle and fountaine of genera- 
tion." He then makes the various characters in the dialogue speak 
to the motion, and one of them, Firmus, ends his speech thus, "And 

^ For further information about the serpent's eggs of the Druids, see Kendrick; they 
were probably fossil echinoderms. 


now for that which remaineth (quoth he and therewith he laughed) 
I will sing unto those that be skilfull and of understanding one holy 
and sacred sentence taken out of the deepe secrets of Orpheus, which 
not onely importeth this much, that the cgge was before the henne, 
but also attributeth and adjudgeth to it the right of eldership and 
priority of all things in the world, as for the rest, let them remaine 
unspoken of in silence (as Herodotus saith) for that they bee exceeding 
divine and mysticall, this onely will I speake by the way; that the 
world containing as it doth so many sorts and sundry kinds of living 
creatures, there is not in manner one, I dare well say, exempt from 
being engendred of an egge, for the egge bringeth forth birdes and 
foules that fiie, fishes an infinit number that swimme, land creatures, 
as lizards, such as live both on land and water as crocodiles, those 
that bee two-footed, as the bird, such as are footlesse, as the serpent, 
and last of all, those that have many feet, as the unwinged locust. 
Not without great reason therefore is it consecrated to the sacred 
ceremonies and mysteries of Bacchus as representing that nature 
which produceth and comprehendeth in itselfe all things". This 
emphatic passage looks at first sight as if it was a statement of 
the Harveian doctrine omne vivum ex ovo. But the fact that no 
mammals are mentioned makes this improbable. Firmus then sits 
down and Senecius opposes him with the well-worn argument that 
the perfect must precede the imperfect, laying stress also on the 
occurrence of spontaneous, i.e. eggless, generation, and on the fact 
that men could find no "row" in eels. Three hundred years later, 
Ambrosius Macrobius handled the question again (see Whittaker), 
and the progress in embryological knowledge could be strikingly 
shown by the difference in treatment. It would be an interesting 
study to make a detailed comparison of them. 

1-6. Galen 

Another fifty years brings us to Galen of Pergamos, second in 
greatness among ancient biologists, though in spite of his multi- 
tudinous writings he does not quite take this high rank in embiyology. 
That knowledge of the development of the foetus was at this time 
specially associated with Peripatetic tradition appears from a remark 
of Lucian of Samosata, Galen's contemporary. In the satire called, 
The Auction of the Philosophies, Hermes, the auctioneer, referring to the 
Peripatetic who is being sold, says, "He will tell you all about the 


shaping of the embryo in the womb". But Galen was now to weld 
together all the biological knowledge of antiquity into his voluminous 
works, and so transmit it to the Middle Ages. 

Most of Galen's writing was done between a.d. 150 and 180. Out 
of the twenty volumes of Kiihn's edition of 1829, l^^s than one is 
concerned with embryology, a proportion considerably less than in 
the case of Aristotle. Galen's embryology is to be found in his 
Trepl (f)V(nKcov Svvdfiecov, On the Natural Faculties, which contains the 
theoretical part, and in his On the Formation of the Foetus, which con- 
tains the more anatomical part. There is also the probably spurious 
treatise et ^mov to Kara <yaa-Tp6<i, On the Question of whether the Embryo 
is an Animal. 

It is important to realise at the outset that Galen was a vitalist 
and a teleologist of the extremest kind. He regarded the living being 
as owing all its characteristics to an indwelling Physis or natural 
entity with whose "faculties" or powers it was the province of 
physiology to deal. The living organism according to him has a kind 
of artistic creative power, a t6xvv> which acts on the things around 
it by means of the faculties, Swd/xei's, by the aid of which each part 
attracts to itself what is useful and good for it, rb oUelov, and 
repels what is not, to aXXorptov. These faculties, such as the "peptic 
faculty" in the stomach and the "sphygmic faculty" in the heart, 
are regarded by Galen as the causes of the specific functions or 
activity of the part in question. They are ultimate biological cate- 
gories, for, although he admits the theoretical possibility of analysing 
them into simpler components, he never makes any attempt to do 
so, and evidently regards such an effort as doomed to failure, unlike 
Roux, whose "interim biological laws" are really conceived of as 
interim. "The effects of Nature", says Galen, "while the animal is 
still being formed in the womb are all the different parts of the body, 
and after it has been born an effect in which all parts share is the 
progress of each to its full size and thereafter the maintenance of 
itself as long as possible." Galen divides the effects of the faculties 
into three. Genesis, Growth, and Nutrition, and means by the first 
what we mean by embryogeny. "Genesis", he says, "is not a simple 
activity of Nature, but is compounded of alteration and of shaping. 
That is to say, in order that bone, nerve, veins, and all other tissues 
may come into existence, the underlying substance from which the 
animal springs must be altered; and in order that the substance so 


altered may acquire its appropriate shape and position, its cavities, 
outgrowths, and attachments, and so forth, it has to undergo a 
shaping or formative process. One would be justified in calling this 
substance which undergoes alteration the material of an animal, just 
as wood is the material of a ship and wax of an image." In this 
remarkable passage, Galen expresses modern views about chemical 
growth and chemical differentiation. 

Galen then goes on to treat of embryogeny in more detail. "The 
seed having been cast into the womb or into the earth — for there is 
no difference — ", he says (see p. 65), "then after a certain definite 
period a great number of parts become constituted in the substance 
which is being generated; these differ as regards moisture, dryness, 
coldness and warmth, and in all the other qualities which naturally 
derive therefrom", such as hardness, softness, viscosity, friability, 
lightness, heaviness, density, rarity, smoothness, roughness, thickness, 
and thinness. "Now Nature constructs bone, cartilage, nerve, mem- 
brane, ligament, vein, and so forth at the first stage of the animal's 
genesis, employing at this task a faculty which is, in general terms, 
generative and alterative, and, in more detail, warming, chilHng, 
drying and moistening, or such as spring from the blending of these, 
for example, the bone-producing, nerve-producing, and cartilage- 
producing, faculties (since for the sake of clearness these terms must be 
used as well) .... Now the peculiar flesh of the liver is of a certain kind 
as well, also that of the spleen, that of the kidneys and that of the 
lungs, and that of the heart, so also the proper substance of the brain, 
stomach, oesophagus, intestines and uterus is a sensible element, of 
similar parts all through, simple and uncompounded. . . . Thus the 
special alterative faculties in each animal are of the same number 
as the elementary parts, and further, the activities must necessarily 
correspond each to one of the special parts, just as each part has its 
special use. . . . As for the actual substance of the coats of the stomach, 
intestine, and uterus, each of these has been rendered what it is by 
a special alterative faculty of nature; while the bringing of these 
together, the combination therewith of the structures that are in- 
serted into them, etc. have all been determined by a faculty which 
we call the shaping or formative faculty; this faculty we also state 
to be artistic — nay, the best and highest art — doing everything for 
some purpose, so that there is nothing ineffective or superfluous, or 
capable of being better disposed." 


Thus the alterative faculty takes the primitive unformed raw 
material and changes it into the different forms represented by the 
different tissues, while the formative faculty, acting teleologically 
from within, organises these building-stones, as it were, into the 
various temples which make up the Acropolis of the completed 
animal. Galen next goes on to speak of the faculty of growth. "Let 
us first mention", he says, "that this too is present in the foetus 
in utero as is also the nutritive faculty, but that at that stage these 
two faculties are, as it were, handmaids to those already mentioned, 
and do not possess in themselves supreme authority." 

Later on, until full stature is reached, growth is predominant, and 
finally nutrition assumes the hegemony. 

So much for Galen's embryological theory. But before leaving the 
treatise On the Natural Faculties, it may be noted that he ascribes a 
retentive faculty to the uterus as well as to the stomach, and explains 
birth as being due to a cessation of action on the part of the retentive 
faculty, "when the object of the uterus has been fulfilled", and a 
coming into action of a hitherto quiescent propulsive faculty. This 
wholesale allotting of faculties can obviously be made to explain 
anything, and is eminently suited to a teleological account such as 
Galen's. It was not inconvenient as a framework within which all 
the biological knowledge of antiquity could be crystallised, but it was 
utterly pernicious to experimental science. Fifteen hundred years later 
it received what would have been the death-blow to any less virile 
theory, at the hands of Moliere in his immortal Malade Imaginaire : 

Bachelirius. Mihi a docto doctore 

Demandatur causam et rationem quare 
Opium facit dormire 
A quoi respondeo 
Quia est in eo 
Virtus dormitiva 
Cujus est nature 
Sensus assoupire. 
Chorus. Bene, bene, bene, bene respondere. 
Dignus, dignus est entrare 
In nostro docto corpore. 
Bene, bene, respondere. 

But to return to Galen. The book on the formation of the embryo 
opens with a historical account of the views of the Hippocratic writers 


with whom Galen was largely in agreement. It goes on to describe 
the anatomy of allantois, amnios, placenta, and membranes with 
considerable accuracy. The embryonic life consists, it says, of four 
stages: (i) an unformed seminal stage, (2) a stage in which the tria 
principia (a concept here met with for the first time) are engendered, 
the heart, liver and brain, (3) a stage when all the other parts are 
mapped out and (4) a stage when all the other parts have become 
clearly visible. Parallel with this development, the embryo also rises 
from possessing the life of a plant to that of an animal, and the 
umbilicus is made the root in the analogy with a plant. The embryo 
is formed, firstly, from menstrual blood, and secondly, from blood 
brought by the umbilical cord, and the way in which it turns into 
the embryo is made clearer as follows: "If you cut open the vein 
of an animal and let the blood flow out into moderately hot water; 
the formation of a coagulum very like the substance of the liver will 
be seen to take place". And in effect this viscus, according to Galen, 
is formed before the heart. 

Galen also taught that the embryo excreted its urine into the 
allantois, and was acquainted with foetal atrophy. He gave a fairly 
correct account of the junction of the umbilical veins with the 
branches of the portal vein, and the umbilical with the iliac arteries, 
of the foramen ovale, the ductus Arantii and the ductus Botalli. He 
maintained that the embryo respired through the umbilical cord, 
and said that the blood passed in the embryo from the heart to the 
lungs and not vice versa. The belief that male foetuses were formed 
quicker than female ones he still entertained, and explained as being 
due to the superior heat and dryness of the male germ. He also 
associated the male conception with the right side and the female 
with the left and asserted that the intra-uterine movements are sooner 
felt in the case of the male than in the case of the female. Dry foods 
eaten by the mother, he thought, would lead to a more rapid develop- 
ment of the foetus than other kinds. 

In this account of the Galenic embryology I have drawn not only 
upon the book on the formation of the foetus, but also upon his 
v7r6fMV7]/jba, Commentary on Hippocrates, his Trepl alricov av/jLTTTco/naTcov, 
On the Causes of Symptoms, and his book Trepl %peta? tmv fjuoplcor, On the 
Use of Parts. It is this latter work that had the greatest influence on the 
ages which followed Galen's Hfe. In the course of seventeen books, he 
tries to demonstrate the value and teleological significance of every 


structure and function in the human and animal body, and to show 
that, being perfectly adapted to its end, it could not possibly be other in 
shape or nature than what it is. At the conclusion of this massive work 
with all its extraordinary ingenuity and labour, he says, "Such then 
and so great being the value of the argument now completed, this 
section makes it all plain and clear like a good epode — I say an epode, 
but not in the sense of one who uses enchantments (eVwSat?) but as 
in the melic poets whom some call lyric, there is as well as strophe 
and antistrophe, an epode, which, so it is said, they used to sing 
standing before the altar as a hymn to the Gods. To this then I 
compare this final section and therefore I have called it by that 
name". This is one of the half-dozen most striking paragraphs in 
the history of biology ; worthy to rank with the remarks of Hippo- 
crates on the " Sacred Disease". Galen, as he wrote the words, must 
have thought of the altar of Dionysus in the Athenian or Pergamene 
theatre, made of marble and hung about with a garland, but they 
were equally applicable to the altar of a basilica of the Christian 
Church with the bishop and his priests celebrating the liturgy at it. 
What could be more charged with significance than this? At the 
end of the antique epoch the biology of all the schools, Croton, 
Akragas, Cos, Cnidus, Athens, Alexandria, Rome, is welded together 
and as it were deposited at the entrance into the sanctuary of 
Christendom. It was the turning-point, in Spengler's terminology, 
between ApoUinian civilisation and Faustian culture. Galen's words 
are the more extraordinary, for he himself can hardly have foreseen 
that the long line of experimentalists which had arisen in the sixth 
century B.C. would come to an end with him. But so it was to be, 
and thenceforward experimental research and biological speculation 
were alike to cease, except for a few stray mutations, born out of 
due time, until in 1453 the city of Byzantium should burst like .a 
ripe pod and, distributing her scholars all over the West, as if by 
a fertilising process, bring all the fruits of the Renaissance into being. 



2-1. Patristic, Talmudic, and Arabian Writers 

We are now at the beginning of the second century a.d. The next 
thousand years can be passed over in as short a time as it has taken 
to describe the embryology of Galen alone. The Patristic writers, 
who on the whole were careful to base their psychology on the 
physiology of the ancients, had little to say about the developing 
embryo. Most of their interest in it was, as would naturally be 
expected, theological; Tertullian, for instance, held that the soul was 
present fully in the embryo throughout its intra-uterine life, thus 
denying that kind of psychological recapitulation which had been 
suggested by Aristotle. "Reply," he says in his De Anima, "O ye 
Mothers, and say whether you do not feel the movements of the 
child within you. How then can it have no soul? " These views were 
not held by other Fathers, of whom St Augustine of Hippo {De 
Immortalitate et de quantitate ahimae) may serve as a representative, for 
he thought that the embryo was "besouled" in the second month 
and "besexed" in the fourth. These various opinions were duly 
reflected in the law, and abortion, which had even been recom- 
mended theoretically by Plato and defended practically by Lysias 
in the fourth or fifth century B.C., now became equivalent to homicide 
and punishable by death. This fact leads Singer to the view that 
the Hippocratic oath is late, perhaps early Christian. The late Roman 
law, which, according to Spangenberg, regarded the foetus as not 
''Homo'", not even '' Infans'\ but only a ''Spes animantis'\ was 
gradually replaced by a stern condemnation of all pre-natal infanti- 
cide. "And we pay no attention", said the Bishops of the Quinisext 
Council, held at Byzantium in 692, "to the subtle distinction as to 
whether the foetus is formed or unformed." Other authorities, follow- 
ing St Augustine, took a more liberal view, and the canon law as finally 
crystallised recognised first the fortieth day for males and the eightieth 
day for females as the moment of animation, but later the fortieth 
day for both sexes. The ''embryo informatus" thus had no soul, the 


^'^ embryo formatus" had, and as a corollary could be baptised. 
St Thomas Aquinas was of opinion that embryos dying in utero might 
possibly be saved : but Fulgentius denied it. As for the ancient belief 
that male embryos were formed twice as quickly as female ones, it 
lingered on until Goelicke took the trouble to disprove it experi- 
mentally in 1723. 

Clement of Alexandria, in his book \6<yo<i TrporpeTTriKO'i Trpo? 
"EX\.7]va'i, has some remarks to make on embryology, but adds nothing 
to the knowledge previously gained. He adopts the Peripatetic view 
that generation results from the combination of semen with menstrual 
blood, and he uses the Aristotelian illustration of rennet coagulating 
milk. Lactantius of Nicomedia, who lived about the date of the 
Nicene Council (a.d. 325) perpetuated the deeply-rooted association 
of male with right and female with left in his book On the work of 
God, De opificio Dei. He also maintained that the head was formed 
before the heart in embryogeny, and seems to have opened hen's 
eggs systematically at different stages, so that to this extent he was 
a better embryologist than Galen. St Gregory of Nyssa, as we have 
already seen (p. 20), evolved a neo-vitalistic theory which he ap- 
plied to the growth of the embryo. 

Late Latin writers, other than the theologians, do not say much 
about it. There is a passage in Ausonius, however, which describes 
the development of the foetus {Eclog. de Rat. puerp.) but it is almost 
wholly astrological. Elsewhere he says: 

juris idem tribus est, quod ter tribus; omnia in istis; 
forma hominis coepti, plenique exactio partu, 
quique novem novies fati tenet ultima finis. 

Idyll II (Gryphus ternarii numeri), 4-6. 
(The power of 3, in 3 times 3 lies too, 
Thus 9 rules human form and human birth, 
And 9 times 9 the end of human life.) 

But this is probably a late echo of the Pythagoreans rather than 
an early prelude to Leonardo da Vinci and the mathematisation of 

That great mass of Jewish writings known as the Talmud, which 
grew up between the second and sixth centuries a.d., also contains 
some references to embryology, and certain Jewish physicians, such 
as Samuel-el-Yehudi, of the second century, are said to have devoted 


special attention to it. The embryo was called peri habbetten (fruit of 
the body), ]a2n ns. It grew through various definite stages: 

(i) golem (formless, rolled-up thing), nbu, 0-1-5 months. 

(2) shefir meruqqdm (embroidered foetus), api» T'Dit. 

(3) ^ubbar (something carried), imi?, 1-5-4 months. 

(4) walad (child), n*?!, 4-7 months. 

(5) walad shel qaydmd (viable child), so'^^p '7tri'?i, 7-9 months. 

(6) ben she-kallu khaddshdw (child whose months have been com- 
pleted), rirnn I'^rir ]n. 

The ideas of the Talmudic writers on the life led by the embryo 
in utero are well represented by the remark, "It floateth like a nut- 
shell on the waters and moveth hither and thither at every touch" 

ms o*» "rtr ':'SDn niia TUNb las •'^lan n»n n'?i rrch ity'^s •'sn lasi 

And the classical passage, "Rabbi Simlai lectured: the babe in its 
mother's womb is like a rolled-up scroll, with folded arms lying 
closely pressed together, its elbows resting on its hips, its heels against 
its buttocks, its head between its knees. Its mouth is closed, its navel 
open. It eats its mother's food and sips its mother's drink: but it 
doth not excrete for fear of hurting" 

bv rT* niioi "rsipa'!^ Q^ith las "'yan n»n n'^in rxh ''V^b's^^ •'in tJ^m 
ittNtr na» nmtyi n'?sis las:^ n»» '?2isi mns "nuai miio rsi rsin ^■'n i"? 

It was thought, moreover, that the bones and tendons, the nails, 
the marrow in the head and the white of the eye, were derived from 
the father, "who sows the white", but the skin, flesh, blood, hair, 
and the dark part of the eye from the mother, "who sows the red". 
This is evidently in direct descent from Aristotle through Galen, and 
may be compared with the following passage from the latter writer's 
Commentary on Hippocrates: "We teach that some parts of the body 
are formed from the semen and the flesh alone from blood. But 
because the amount of semen which is injected into the uterus is 
small, growth and increment must come for the most part from the 
blood". It might thus appear that, just as the Jews of Alexandria 
were reading Aristotle in the third century B.C., and incorporating 




him into the Wisdom Literature, so those of the third century a.d. 
were reading Galen and incorporating him into the Talmud. As for 
God, he contributed the life, the soul, the expression of the face, the 
functions of the different parts. This participation of three factors in 
generation, male, female, and god, is exceedingly ancient, as may 
be read in Robertson Smith. Some Talmudic writers held that 
development began with the head, agreeing with Lactantius, and 
others that it began at the navel, agreeing with Alcmaeon. Weber 
has given an account of the Talmudic beliefs about the infusion of 
the soul into the embryo. They do not seem to have embodied any 
new or striking idea. 

Although the Talmud contained certain references of embryo- 
logical interest, the first Hebrew treatise on biology was not composed 
till the tenth century, when Asaph Judaeus or Asaph-ha-Yehudi 
wrote on embryology about a.d. 950. His MSS. are exceedingly 
rare, but, according to Gottheil's description, they contain several 
sections on embryology. Steinschneider has given another descrip- 
tion of them. For further details on the whole subject of Jewish 
embryology see Macht. 

Arabian science, so justly famed for its successes in certain branches, 
was not of great help to embryology. Abu-1-Hasan ' Ali ibn Sahl ibn 
Rabban al-Tabari, a Moslem physician who flourished under the 
Caliphate of al-Mutawakldl about a.d. 850, wrote a book called 
The Paradise of Wisdom, in which an entire part was devoted to 
embryology, all the more interesting as it is a mixture of Greek and 
ancient Indian knowledge. Browne gives a description of it. Ibn 
Rabban's contemporary, Thabit ibn Qurra, is also said to have 
written on embryology. The great Avicenna, or, to give him his 
proper name, Abu 'Ali-1-Hasan ibn 'Abdallah ibn Sina, who lived 
from 978 to 1036, devoted certain chapters of his Canon Medicinae to 
the development of the foetus, but added nothing to Galen. His 
contemporaries, Abu-1-Qasim Maslama ibn Ahmad al-Majriti and 
Arib ibn Said al-Katib, a Spanish Moslem, wrote treatises on the 
generation of animals, but neither has survived. 

What was alchemy doing all this time? It was engaged on many 
curious pursuits, but among them the interpretation of embryonic 
development was not one. Alchemical texts before the tenth century 
do make reference to eggs from time to time, but it is safe to say 
never with any trace of an interest in the development of the embryo 


out of them. One example taken from Berthelot's collection will 
suffice; it comes from the "6th book of the Philosopher" (Syriac). 

To make water of eggs 

Take as many eggs as you wish, break them and put the whites in a 
glass flask, place this in another vessel and surround it with fresh horse- 
dung up to the neck of the vessel. Leave it so for 15 days changing the 
dung every 5 days. Then distil the liquid in an alembic and taking a 
pound of the distillate add lime of eggs 2 ozs. Shake well and distil again. 
Do this 4 times. Take then of elixir of arsenic, 2 parts, of sulphur i part, 
of pyrites and magnesia, each i part. Pound in a mortar and add to the 
final distillate from the eggs. Do this for 7 days always working in the 
sunlight, once at sunrise, once in the middle of the day, and once at 
sunset. When this has been done, dry the mixture, pound it, and set it 

I could only find one reference to the embryo in a hen's egg among 
the vast number of alchemical directions of this time, and then only 
as a constituent of the egg which must be discarded. As we shall see, 
it is not until after the time of Paracelsus that the notion of applying 
chemical methods to eggs or embryos arises at all. 

2-2. St Hildegard: the Lowest Depth 

Not long after the death of Avicenna, St Hildegard was born. 
She lived from 1098 to 1180, and was Abbess successively of Disi- 
bodenberg and Bingen in the Rhineland. Her treatises on the world, 
which are an extraordinary medley of theological, mystical, scientific 
and philosophical speculation, have been described in detail by 
Singer, and, though in the books. Liber Scivias and Liber Divinorum 
Operum simplicis hominis, there is little of embryological interest, yet 
she does give an account of development and especially of the entry 
of the soul into the foetus. 

This is illustrated in Plate HI taken from the Wiesbaden Codex B 
of the Liber Scivias. The soul is here shown passing down from heaven 
into the body of the pregnant woman and so to the embryo within 
her. The divine wisdom is represented by a square object with its 
angles pointing to the four corners of the earth in symbol of stabihty. 
From it a long tube-Hke process descends into the mother's womb 
and down it the soul passes as a bright object, "spherical" or "shape- 
less", illuminating the whole body. The scene shows the mother in 
the foreground lying down ; inside her there are traces of the foetal 
membranes; behind this ten persons are grouped, each carrying a 


vessel, into one of which a fiend pours some noxious substance from 
the left-hand corner. St Hildegard describes and expounds the scene 
as follows: "Behold, I saw upon earth men carrying milk in earthen 
vessels and making cheeses therefrom. Some was of the thick kind 
from which firm cheese is made, some of the thinner sort from which 
more porous cheese is made, and some was mixed with corruption 
and of the sort from which bitter cheese is made. And I saw the like- 
ness of a woman having a complete human form within her womb. 
And then by a secret disposition of the most high craftsman, a fiery 
sphere having none of the lineaments of a human body possessed the 
heart of the form and reached the brain and transfused itself through 
all the members. . . . And I saw that many circling eddies possessed 
the sphere and brought it earthward, but with ever renewed force 
it returned upwards and wailed aloud, asking, 'I, wanderer that I 
am, where am I?' 'In death's shadow.' 'And where go I?' 'In the 
way of sinners.' 'And what is my hope? ' ' That of all wanderers.' . . . 
As for those whom thou hast seen carrying milk in earthen vessels, they 
are in the world, men and women alike, having in their bodies the 
seed of mankind from which are procreated the various kinds of 
human beings. Part is thickened because the seed in its strength 
is well and truly concocted and this produces forceful men to whom 
are allotted gifts both spiritual and carnal.. . .And some had cheeses 
less firmly curdled, for in their feebleness they have seed imperfectly 
tempered and they raise offspring mostly stupid, feeble, and use- 
less, . . . And some was mixed with corruption . , . for the seed in that 
brew cannot be rightly raised, it is invalid, and makes misshapen 
men who are bitter distressed and oppressed of heart so that they 
may not lift their gaze to higher things. . . .And often in forgetfulness 
of God and by the mocking devil a mistio is made of the man and 
the woman and the thing born therefrom is deformed, for parents 
who have sinned against me return to me crucified in their children". 
We have already traced the wanderings of the cheese-analogy, 
which, beginning fresh with Aristotle, was taken to Alexandria and 
incorporated in the Wisdom Literature, and so found its way to the 
Arabic of 'Ali ibn a'1-Abbas al-Majusi, or Haly-Abbas, as he was 
known in the West, a Persian. His Liber Totius appeared in Latin 
in 1523, but had been translated much earlier, at Monte Cassino 
between 1070 and 1085, by Constantine the African, who called it 
Liber de Humana Natura, and gave it out to be his own work. Thus 


(Wiesbaden Codex B) showing the descent of the soul into the embryo {ca. 1 150 a.d.). 


St Hildegard obtained it, and worked it up into one of her visions. 
At this point embryology touched, perhaps, its low-water mark. But 
a great man was at hand, destined to carry on the Aristotelian 
tradition and to add to it much of originality, in the shape of Albertus 
of Cologne. Before speaking of him, however, a word must be said 
about that very queer character, Michael Scot (i 178-1234), who, 
according to Gunther, "appeared in Oxford in 1230 and experi- 
mented with the artificial incubation of eggs, having got an Egyptian 
to teach him how to incubate ostriches eggs by the heat of the Apulian 
sun". That "muddle-headed old magician", as Singer rightly calls 
him, was not the man to profit by it, but the point is interesting, 
especially as an Egyptian is mentioned. Haskins, in his curious 
studies of the scientific atmosphere of the court of the Emperor 
Frederick II of Sicily, has shown Scot, newly arrived fi"om his 
alchemical studies in Spain, assisting that very learned and unor- 
thodox monarch in his artificial incubation experiments. 

2-3. Albertus Magnus 

Albertus Magnus of Cologne and Bollstadt was born in 1206, 
and died in 1280, six years after his favourite disciple, St Thomas 
Aquinas. The greater part of his life was spent in study and teaching 
in one or other of the houses of the Dominican friars, to which he 
belonged, though for a time he was Bishop of Regensburg. Albert 
resembles Aristotle in many points, but principally because he pro- 
duced biological work with, as it were, no antecedents. Just as 
Aristotle's contributions to embryology were preceded by no more 
than the diffuse speculations of the Ionian nature-philosophers, so 
Albert's came immediately after the dead period represented by the 
visions of St Hildegard. In many ways, Albert's position was much 
less conducive to good work than Aristotle's. 

Albert follows Aristotle closely throughout his biological writings, 
quoting him word for word in large amounts, but the significant 
thing is that he does not follow him slavishly. He resembled Aristotle 
in paying much attention to the phenomena of generation, as a rough 
computation shows, Aristotle devoting 37 per cent, of his biological 
writings to this subject, and Albert 31 per cent., to which Galen's 
7 per cent, may with interest be compared. Albert is extremely 
inferior to Aristotle, however, in point of arrangement; for Aristotle, 
although some of his books, such as the De Generatione Animalium, 


are sufficiently confused and repetitive, does yet succeed in infusing 
a clarity and incisiveness into his style. Albert, on the other hand, 
allows his argument to wander through his twenty-six books De 
Animalibus in the most complex convolutions, so that the sections on 
generation and embryology are found indiscriminately in the first, 
sixth, ninth, fifteenth, sixteenth, and seventeenth. In Book i he gives 
a kind of summary or skeleton of his views on the embryo. These 
follow Aristotle fairly closely; thus, he accepts the AristoteHan classi- 
fication of animals according to their manner of generation, and 
thinks still that caterpillars are immature eggs ; he derives the embryo 
from the white, not the yolk, and he explains why soft-shelled eggs, 
being imperfect, are of one colour only. But there are new observa- 
tions; for instance, he describes an ovum in ovo, which he has seen, 
calling it a natura peccatis, and he speaks definitely of the seed of 
the woman, thus departing from Peripatetic opinion, and adopting 
the Epicurean view. The female seed, he thinks, suflfers coagulation 
like cheese by the male seed, and to these two humidities there must 
be added a third, namely, the menstrual blood (corresponding to 
the yolk in the case of the bird). "When these three humidities 
therefore have been brought into one place, all the similar members 
except the blood and fat are formed from the two humidities of which 
one generates actively but the other passively. But the blood which is 
attracted for the nutriment of the embryo is double in virtue and 
double in substance. For a certain part of the blood is united with 
the sperm in such a way that it takes on some of the virtue of the 
seed because a certain part of the spermatic humour remains in it 
and from this are begotten the teeth and for this reason they grow 
again if they are pulled out at an age near the time of sperm-making 
and do not grow again at an age remoter from this, at which the 
virtue of the first generating principle has vanished from the blood. 
But another part of the blood is of twofold or threefold substance 
and from the thick part of the blood itself is generated the flesh. 
And this flows in and flows out and grows again if rubbed away. 
From the watery part of the same blood or of the nutritive humour 
are generated the fat and oil and this flows in and out more easily 
than the flesh itself, but other parts of the blood are its refuse and 
impurities and are not attracted to the generation of any part of the 
animal, but having been collected until birth are expelled with the 
embryo from the uterus in the foetal membranes, like the remnants 


in the hen's egg after the chick has hatched. There is a similar virtue 
in the liver and heart of animals which organs after the animals are 
born form the flesh and fat from food in accordance with its twofold 
substance, and expel the refuse as we said before," 

In the sixth book, Albert contradicts Aristotle's opinion that male 
chick develops out of the sharp-ended egg, and one hopes that he 
is going to say there is no relationship between egg-shape and sex, 
but no, he goes on to say that the Aristotelian statement rested on a 
textual error (in which he was quite wrong), so that really Aristode 
agreed with Avicenna in saying that the males always develop from 
the more spherical eggs because the sphere is the most perfect of figures 
in solid geometry. These errors had a most persistent life : Horace has 
a passage in which they appear — 

longa quibus facies ovis erit, ilia memento 
ut suci melioris, et ut magis alma rotundis 
ponere: namque marem cohibent callosa vitellu.m. 

(When you would feast upon eggs, make choice of the long ones ; they 
are whiter and sweeter and more nourishing than the round, for being 
hard they contain the yolk of the male.) 

They were finally abolished by two naturalists, Giinther and Biihle, 
who took the trouble to disprove them experimentally in the eigh- 
teenth century. Albertus refers here to artificial incubation: "For 
the alterative and maturative heat", he says, "of the egg is in 
the egg itself and the warmth which the bird provides is altogether 
external [extrinsecus est amminiculans] since in certain hot countries 
the eggs of fowls are put under the surface of the earth and come 
to completion of their own accord, as in Egypt, for the Egyptians 
hatch them out by placing them under dung in the sunlight". 
Next he speaks of monsters and of the modes of corruption 
of eggs which he divides into four: (i) decomposition of white, 
(2) decomposition of yolk, (3) bursting of the yolk-membrane, 
(4) antiquitas ovi. "And from the second cause it sometimes happens ", 
he says, "that in the corruption of the humours certain igneous 
parts are carried blazing to the shell of the egg and distribute them- 
selves over it so that it shines in the dark like rotten wood; as 
happened in the case of that egg^ which Avicenna said he saw in 
the city called Kanetrizine in the country of the Gorascenes." Albert 

^ See on this subject Zach. 



is inclined to think that astrological influences may have an effect 
on foetal life, but he treats the suggestion with considerable scepticism, 
although he believes that thunder and lightning kill the embryos of 
fowls (a popular belief to which Fere tried not long ago to give a 
scientific foundation), and he regards the embryo of the crow as 
especially susceptible, though on what grounds he does not say. 

The fourth chapter of the first tractate of the sixth book contains 
Albert's description of development of the chick, and is extremely 
interesting. He makes two principal mistakes: {a) he describes a 
quite non-existent fissure in the shell by which the chick may emerge, 
{b) he maintains that the yolk ascends after a day or two into the 
sharp end of the egg, adducing as the reason that there is found 
there more heat and formative force than elsewhere. On the other 
hand, he correctly describes {a) the pulsating drop of blood on the 
third day, and {b) he identifies it with the heart with its systolen et 
dyastolen sending out the "formative virtue" to all the parts of the 
growing body. He notices [c) that the differentiation of the chick at 
first proceeds rapidly and later more slowly. But the most notable 
characteristic of Albert's embryology is the way in which he is 
hampered by his inability to invent a technical terminology. Singer 
has studied the way in which anatomical terms, such as "syrach", 
etc., came into use, but whatever the causes were which produced 
them, they did not operate much in Albert's mind. He represents 
the point beyond which embryology could not advance, until it 
had created a new set of terms. This is well illustrated by the 
following passage: 

"But fi'cni the drop of blood", he says, "out of which the heart is 
formed, there proceed two vein-like and pulsatile passages and there is in 
them a purer blood which forms the chief organs such as the liver and 
lungs and these though very small at first grow and extend at last to the 
outer membranes which hold the whole material of the egg together. There 
they ramify in many divisions, but the greater of them appears on the 
membrane which holds the white of the egg within it [the allantois]. The 
albumen, at first quite white, is changed owing to the power of the vein 
almost to a pale yellow-green tint [palearem colorem]. Then the path of 
which we spoke proceeds to a place in which the head of the embryo is 
found carrying thither the virtue and purer material from which are 
formed the head and the brain, which is the marrow of the head. In 
the formation of the head also are found the eyes and because they are of 
an aqueous humidity which is with difficulty used up by the first heat 
they are very large, swelling out and bulging from the chick's head. A short 


time afterwards, however, they settle down a little and lose their swelling 
owing to the digestive action of the heat — and all this is brought about by 
the action of the formative virtue carried along the passage which is 
directed to the head, but before arriving there is separated and ramified 
by the great vein of the albumen-membrane, as may be clearly seen by 
anyone who breaks an egg at this time and notes the head appearing in 
the wet part of the egg and at the top of the other members. For what 
appears first in the making of a foetus are the upper parts because they are 
nobler and more spiritual being compacted of the subtler part of the egg 
wherein the formative virtue is stronger. When this happened one of the 
aforementioned two passages which spring from the heart branches into 
two, one of them going to the spiritual part which contains the heart and 
divides there in it carrying to it the pulse and subtle blood from which the 
lungs and other spiritual parts are formed, and the other going through 
the diaphragm \dyqfracmd\ to enclose within it at the other end the yolk 
of the Qgg, around which it forms the liver and stomach. It is accordingly 
said to take the place of the umbilicus in other animals and through it food 
is drawn in to supply the flesh for the chick's body, for the principle of genera- 
tion of the radical members of the chick comes from the albumen but the food 
from which is made the flesh filling up all the hollows is from the yolk." 

After ten days, Albert goes on to say, all the constituent organs 
are mapped out and the head is greater then than the rest of the 
body put together. He observes that the yolk liquefies early in 
development and that slimy concretions are present in the allantoic 
fluid later on (uric acid). But the passage quoted does demonstrate 
that before further progress could be made some better name must 
be found than "the interior membrane to which the first vessel 
proceeds" for a given structure. 

Albert, however, was accomplishing a good work. One of his best 
amplifications of Aristotle was his description of the relationship 
between yolk and embryo in fishes. Just as his words about the chick 
demonstrate that he must have opened hen's eggs at different stages 
during incubation, so his words about fish eggs show that he must 
have dissected and examined them also. Thus (Book vi, tractate 2, 
chap, i) he says, "Between the mode of development [anathomiam 
generationis] of birds' and fishes eggs there is this diflference ; during 
the development of the fish the second of the two veins which extend 
from the heart does not exist. For we do not find the vein which 
extends to the outer covering of the eggs of birds which some wrongly 
call the umbilicus because it carries the blood to the outside parts, 
but we do find the vein which corresponds to the yolk vein of birds, 
for this vein imbibes the nourishment by which the limbs increase. 


Therefore the generation of the fish embryo begins from the sharp 
end of the egg like that of birds and channels extend from the heart 
to the head and eyes and first in them appear the upper parts. 
As the growth of the young fish proceeds the yolk decreases in 
amount being incorporated into the members and it disappears en- 
tirely when development is complete. The beating of the heart, which 
some call panting, is transmitted through the pulsating veins to the 
lower part of the belly carrying life to the inferior members. While 
the young fish are small and not yet fully developed they have veins 
of great length which take the place of the umbilicus, but as they grow 
these shorten till they contract into the body by the heart as has 
been said about birds. The young fish are enclosed in a covering 
just like the embryos of birds, which resembles the dura mater and 
beneath it another containing the foetus and nothing else, while 
between the two there is the moisture rejected during the creation of 
the embryo". Albert also described ovoviviparous fishes but it is more 
difficult in that case to tell whether he had himself seen and dissected 
them. He notes also the prodigality of nature in producing so many 
marine eggs only destined to be eaten. 

In Books IX and xv he treats of the Galenic views on generation 
and insists again that there is a seed provided by the female. In 
Book XVI he gives his opinions about the animation of the embryo, 
quoting the views of the ancients as given in Plutarch, e.g. Alexander 
the Peripatetic, Empedocles, Anaxagoras, Theodorus and Theo- 
phrastus, the Peripatetics, Socrates, Plato, the Stoics, Avicenna, and 
Aristotle, "who saw the truth", but— and it is interesting to notice 
it — never the Christian Fathers, whose writings must have been well 
known to him. In discussing the Aristotelian views he compares the 
menstrual blood to the marble and the semen to the man with a 
chisel in his hand. 

On the question of epigenesis and preformation, he follows 
Aristotle almost word for word, using the same analogies, such as 
the "dead eye" and the sleeping mathematician. Here his scho- 
lasticism comes out clearly, for in rejecting altogether the theory 
that one part being formed then forms the next part, he says, not 
that A would have to be in some way like B, but is not, as Aristotle 
had, but simply "^Generans et generatum, est simul esset et non esset, 
quod omnino est impossibile''^ — a high-handed and very unscientific 
manner of settling the question. In conformity with his theology and 


in contradistinction from Aristotle he makes the vegetative and 
sensitive souls arrive automatically into the embryo but the rational 
soul only by a direct act of God. 

His mammalian embryology presents some points of interest. He 
follows Hippocrates ("Ypocras") in an account of the co-operation 
of heat and cold in member-formation, and he holds very enlightened 
views about foetal nutrition, "It appears therefore that the embryo 
hangs from the cord and that the cord is joined with the vein and 
that the vein extends through the uterus and has blood running 
through it to the foetus like water through a canal. Round the embryo 
there are membranes and webs as we have seen. But those who think 
that the embryo is fed by little bits of flesh through the cord are 
wrong and lie, because if this were the case with man it would happen 
also with other animals and that it does not do so anybody can find 
out by investigation [per anathomyani].'" 

Finally, it is typical that in Book xvii Albert repeats what he has 
already said in Book vi about the generation of the hen out of the 
tgg all over again with slight changes, but he adds the significant 
biochemical remark that "eggs grow into embryos because their 
wetness is like the wetness of yeast". The importance of Albert in 
the history of embryology is clear. With him the new spirit of in- 
vestigation leapt up into being, and, though there were many years 
yet to pass before Harvey, the modern as opposed to the ancient 
period of embryology had begun. Albert's writings were often 
copied and printed in the next few centuries, and even as late as 1601 
De Secretis Mulierum, an epitome of his books on generation, was 
published. In some sense, it still is, as it forms the backbone of the 
little book Aristotle's Masterpiece, of which thousands of copies are sold 
in England every year. The copy of the De Secretis in the Caius College 
Library has written across the title-page in faded ink "Simulacra 
sanctitas, duplex iniquitas, Nathan Emgross, Nov. 20. 161 3." But in 
spite of Mr Emgross, Albertus, rightly called Magnus, has had the 
happy fate of being beatified both by the Church and by science. 

2-4. The Scholastic Period 

St Thomas Aquinas (i 227-1 274) incorporated the Aristotelian 
theories of embryology into his Summa Theologica especially under 
the head De propagatione hominis quantum ad corpus. There are some 
striking passages, such as "The generative power of the female 


is imperfect compared to that of the male; for just as in the crafts, 
the inferior workman prepares the material and the more skilled 
operator shapes it, so likewise the female generative virtue provides 
the substance but the active male virtue makes it into the finished 
product". How admirably this expresses the dominating sentiment 
of the Middle Ages! Aristotle might make a distinction between 
matter and form in generation, but the mediaeval mind, with its 
perpetual hankering after value, would at once enquire which of the 
two was the higher, the nobler, the more honourable. 

St Thomas' theory of embryonic animation was complicated. He 
had a notion that the foetus was first endowed with a vegetative 
soul, which in due course perished, at which moment the embryo 
came into the possession of a sensitive soul, which died in its turn, 
only to be replaced by a rational soul provided directly by God, 
This led him into great difficulties, for, if this scheme were true, it 
was difficult to say that man generated man at all; on the contrary 
he could hardly be said to generate more than a sensitive soul which 
died before birth, and, on this view, what was to happen to original 
sin? As Harris has put it, Plato had said that the intellect was the 
man, using the body as a boatman uses a boat. Averroes had said 
precisely the opposite, namely, that the essence of humanity was in 
the body, and that the intellect was something extrinsic, not limited 
to the individual, but common to the race. Aristotle had taken the 
middle position, and given a soul to plants and animals, but, in 
doing so, he had made it into a vital rather than a psychological 
principle. The task of combining this -^vxv with the anima of the 
Fathers was what scholastic philosophy had before it. No wonder 
that St Thomas' account of embryonic animation was open to 
criticism. An echo of it appears in a poem of Jalalu'd-Din Rumi 
( 1 207-1 273), the greatest of the Persian Sufi poets, and an exact 
contemporary of St Thomas Aquinas : 

I died from mineral and plant became: 
Died from the plant, and took a sentient frame; 
Died from the beast, and donned a human dress; 
When by my dying did I e'er grow less? 

Duns Scotus (i 266-1 308) objected to St Thomas' theory on the 
grounds already mentioned, and he himself abandoned the vegetative 
and sensitive souls altogether in his De Rerum Principio. This solution 


was no better than that of St Thomas, for, agreeing with the latter 
as Duns did that the rational soul was not an ordinary form "educed " 
from the "potentiality" of the material, but rather an ad hoc creation 
of God, injected by divine power into the embryo at the appropriate 
moment, it was difficult to see how the spiritual effects of Adam's 
fall could be transmitted to the men of each generation. It was as 
if only acquired characteristics were inherited. But the further course 
of theological embryology need not be pursued here ; it runs in every 
century parallel with true scientific embryology, and it is not my 
purpose to do more than take a glance at its progress from time to time. 
In the Speculum Naturale, which was written about 1250, by Vincent 
of Beauvais, the embryology of Constantine the African appears 
again, and the embryology of Aristotle, Galen, and the scholastics 
is to be found in Dante Alighieri (i 265-1 321), who dealt with the 
subject in his Convivio, and especially in the Divina Commedia. In 
Canto XXV of the Purgatorio, Statins (the personification of human 
philosophy enlightened by divine revelation) is made to speak to 
the poet thus: "If thy mind, my son, gives due heed to my words 
and takes them home, they will elucidate the question thou dost ask. 
Perfect blood which is in no case drawn from the thirsty veins, but 
which remains behind like food that is removed from table, receives 
in the heart informing power for all the members of the human body, 
like the other blood which courses through the veins in order to be 
converted into those members. After being digested a second time 
it descends to the part whereof it is more seemly to keep silence than 
to speak, and thence it afterwards drops into the natural receptacle 
(the uterus) upon another's blood ; there the one blood and the other 
mingle. One is appointed to be passive, the other to be active 
according to the perfect place whence it proceeds (the heart). And 
being united with it, it begins to operate, first by coagulating it, and 
then by vivifying that to which it has given consistency, so that there 
may be material for it to work upon [e poi avviva, Cib che per sua materia 
fe' constare]. The active power having become a (vegetative) soul like 
that of a plant — only differing from it in this, that the former is in 
progress while the latter has reached its goal — thereafter works so 
much that it moves and feels like a sea-fungus and as the next stage 
it takes in hand to provide with organs the faculties which spring 
from it. At this point, my son, the power which proceeds from the 
heart of the begetter is expanded and developed, that power in which 


Nature is intent on forming all the members, but how from being 
an animal it becomes a child, thou seest not yet, moreover this is 
so difficult a point that formerly it led astray one more wise than thou 
[Averroes], so that in his teaching he separated the active 'intellect' 
from the soul because he could not see any organ definitely appro- 
priated by it. Open thy heart to the truth and know that as soon 
as the brain of the foetus is perfectly organised, the Prime Mover, 
rejoicing in this display of skill on the part of Nature, turns him 
towards it and infuses a new spirit replete with power into it which 
subsumes into its own essence the active elements which it finds al- 
ready there, and so forms one single soul which lives and feels and 
is conscious of its own existence. And that thou mayst find my saying 
less strange, bethink thee how the heat of the sun passing into the 
juice which the grape distils, makes wine". 

Having said this. Statins, Virgil and Dante pass on to the seventh 
ledge in Purgatory. It is interesting to see how Dante emphasises 
the dynamic teleological side of Aristotle and practically speaks of 
the soul enfleshing itself and arranging organs for its faculties. The 
reference to Averroes is explained by the fact that Averroes was a 
Traducianist, and held that all the soul was generated by man at 
the same time as the body, whereas both St Thomas and Dante, as 
Creationists, held that each fresh soul was a special creation of God 
inserted by him into the brain of the embryo. The mention of Dante's 
contemporary, Mondino de Luzzi (1270-1326), brings us to the more 
practical aspects of embryology at this period. Mondino is the most 
outstanding figure among the Bolognese anatomists of what is really 
the first period of the revival of biology. After him, as we shall see, 
biology languished for a couple of centuries until the advent of such 
men as Ulysses Aldrovandus in the sixteenth century, and Singer has 
shown that this was probably due to the fact that anatomy professors 
did not dissect in person. A fortiori embryotomy was infrequent. 

But Mondino's Anathomia, published in 13 16, contained statements 
about the organs of generation which were rather important. He 
retains the notion of the seven-celled uterus, which had been intro- 
duced by Michael Scot, but he adopts a reasonable compromise 
between the opinions of Galen and Aristotle on the physiology of 
embryo formation. The distance between him and Leonardo da 
Vinci (1452-1519) would, however, be estimated rather at five or six 
centuries than at the century and a quarter that it actually was. 


2-5. Leonardo da Vinci 

Leonardo was not alone among the artists of the Renaissance in 
his anatomical interests, for Michael Angelo, Raphael, Diirer, 
Mantegna, and Verrochio all made dissections in order to increase 
their knowledge of the human body. But he penetrated more curiously 
into biology than they did, and he will always remain one of the 
greatest of biologists, for he first introduced the quantitative outlook. 
In this he was some four hundred years before his time. 

Leonardo's embryology is contained in the third volume of his 
notebooks, Quaderni d' Anatomia, published in facsimile by the ad- 
mirable labours of three Norwegian scholars, Vangensten, Fohnahn 
and Hopstock, in 191 1. His notebooks are a remarkable, and, indeed, 
charming miscellany of anatomical drawings, physiological diagrams, 
architectural and mechanical sketches and notes such as "Shirts, 
hose, and shoes", "Go and see Messer Andreas", "get coal", "the 
supreme fool (is the) necromancer, and enchanter". 

His dissections of the pregnant uterus and its membranes are 
beautifully depicted, as can be seen from the figures which are here 
reproduced (Plate IV). He was acquainted with amnios and chorion, 
and he knew that the umbilical cord was composed only of vessels, 
though he seems to have thought the human placenta was cotyle- 
donous. There is one drawing which the editors suppose to represent 
the developing hen's egg, but I do not feel that this ascription is likely. 
Indeed, Leonardo worked with eggs much less than with mammalian 
embryos, though there are references to the former. "See how birds 
are nourished in their eggs", he says in one place, to remind himself, 
perhaps, of possible experiments, and, elsewhere, "Chickens are 
hatched by means of the ovens of the fireplace". Again, "Ask the 
wife of Biagino Crivelli (was she the Lucrezia Crivelli, whose portrait 
Leonardo painted?) how the capon rears and hatches the eggs of the 
hen when he is inebriated", a subject recently reopened by Lienhart. 
"You must first dissect the hatched egg before you show the difference 
between the human liver in foetus and adult." Leonardo perpetuates 
a persistent error in the note, "Eggs which have a round form 
produce males, those which have a long form produce females". 

Concerning the mammalian foetus, he says, "The veins of the 
child do not ramify in the substance of the uterus of its mother but 
in the placenta which takes the place of a shirt in the interior of the 


uterus which it coats and to which it is connected but not united by 
means of the cotyledons". Thus in one sentence Leonardo falls into 
a mistake in saying that the human placenta is cotyledonous, but 
at the same time asserts a fact which it took all the ingenuity of the 
seventeenth century to prove to be true, namely, that the foetal 
circulation is not continuous with that of the mother, for the placenta 
is only connected to the uterine wall and not united with it. "The 
child", Leonardo goes on to say, "lies in the uterus surrounded with 
water, because heavy things weigh less in water than in the air 
and the less so the more viscous and greasy the water is. And then 
such water distributes its own weight with the weight of the creature 
over the whole body and sides of the uterus." The tendency towards 
quantitative and mathematical explanations is apparent at once. 

Further notes are, "Note how the foetus breathes and how it is 
nourished through the umbilical cord and why one soul governs two 
bodies, as you see the mother desiring food and the child remaining 
marked (by a given amount of growth) because of it. Avicenna 
pretends that the soul generates the soul and the body the body. 
Per errata^'. The child, says Leonardo, secretes urine while still in 
utero, and has excrement in its intestines; at four months it has chyle 
in its stomach, made perhaps from menstrual blood. But it has no 
voice in utero, "when women say that the foetus is heard to weep 
sometimes within the uterus, this is rather the sound of some flatus . . . ". 
Nor does it breathe there (on this point Leonardo contradicts him- 
self). "The child does not respire within the body of its mother 
because it lies in water and he who breathes in water is immediately 
drowned." "Breathing is not necessary to the embryo because it is 
vivified and nourished by the life and food of the mother." Nor does 
the embryonic heart beat. To us the statement that there is no 
respiration in the uterus is obviously false, but we mean by the word 
tissue respiration, whereas in Leonardo's time pulmonary respiration 
was intended; he was therefore perfectly right in denying that the 
embryo breathed, as certain anatomists before him had asserted. 

His only reference to the soul runs thus: "Nature places in the 
bodies of animals the soul, the composer of the body, i.e. the soul 
of the mother, which first composes, in the womb, the shape of man 
and in due time awakens the soul which shall be the inhabitant there- 
of, which first remains asleep and under the tutelage of the soul of 
the mother which through the umbilical vein nourishes and vivifies 


vf Hi^l 


O V^xf^rtl 

V-..,'.'.^/ I »-^ '•' 

•V 'j'.'/** •»T^'"(' ''♦' 

{QUADERNI D' ANATOMIA), ca. 1490 a.d. 


it". This is not very revolutionary. But Leonardo was the first 
embryologist to make any quantitative observations on embryonic 
growth ; he defined, for instance, the length of a full-grown embryo 
as one braccio and the adult as three times that. "The child", he 
says, "grows daily far more when in the body of its mother than 
when it is outside of the body and this teaches us why in the first 
year when it finds itself outside the body of the mother, or, rather, 
in the first 9 months, it does not double the size of the 9 months 
when it found itself within the mother's body. Nor in 18 months 
has it doubled the size it was 9 months after it was born, and thus 
in every 9 months diminishing the quantity of such increase till 
it has come to its greatest height." Here Leonardo touches on one 
of the most modern quantitative aspects of embryology, and one 
almost expects to see him exemplify his words with a graph until 
one remembers with a shock that he lived two centuries before 
Descartes and five before Minot. His numerical data may also have 
included figures about the relative sizes of the parts, and the germ 
of the line of research so successfully pursued by Scammon in our 
own times may be found in the note "The liver is relatively much 
larger in the foetus than in the grown man". Other quantitative 
notes concern the length of the embryonic intestines as in the laconic 
"20 braccia of bowels" and the statement that "the length of the 
umbilical cord always equals the length of the foetal body in man 
though not in animals".^ 

He said little about heredity, but in one place he mentions a case 
of sexual intercourse between an Italian woman and an Ethiopian, 
the outcome of which assured him that blackness was not due to the 
direct action of the sun and that the "seed of the female was as potent 
as that of the male in generation". Finally, the best instance of the 
wideness of his thought appears in the note, "All seeds have an um- 
bilical cord which breaks when the seed is mature. And similarly 
they have matrix and secundines as the herbs and all the seeds 
which grow in shells show". We have met this idea before in Hippo- 
crates of Cos, and we shall find it again in Nathaniel Highmore. 

It is no coincidence that pictures of weights and cogs and pulleys 
stand side by side in Leonardo's notes with anatomical drawings of 
the embryo. As Hopstock says, "Leonardo arrives at the conclusion 
that there is but one natural law which governs the world. Necessity. 

^ Leonardo would have enjoyed Fog's statistical study of 8000 umbUical cords (1930). 


Necessity is Nature's master and guardian, it is Necessity that makes 
the eternal laws". If Aristotle is the father of embryology regarded 
as a branch of natural history, Leonardo is the father of embryology 
regarded as an exact science. 

2-6. The Sixteenth Century: the Macro- Iconographers 

After such a man, the writings of his contemporaries, such as the 
mythical Johannes de Ketham, Alessandro Achillini and Gabriele de 
Gerbi, appear beyond description inferior. De Ketham's embryology 
has been described by Ferckel. De Gerbi included in his Liber 
Anatomiae corporis humani et singulorum membrorum illius a section 
entitled De Generatione Embrjonis, but there is nothing to be said 
about it except that it is a verbose compilation of the views of 
Aristotle and Galen taken from Avicenna. The work of Nolanus in 
1532 presents certain points of interest, but it is of little importance. 
Petrus Crescentius in his work on husbandry of 1548 mentions 
artificial incubation in ovens, but rather as a lost art. About this 
time also Hieronymus Dandinus Cesenas, a Jesuit, wrote a treatise 
on Galen's division of organs into white and red, those proceeding 
from the semen and those proceeding from the blood: it is cited by 
Aldrovandus, but I have not been able to consult it. 

The most remarkable feature of the first half of the century was 
the encyclopaedic group of zoologists which now arose. Thus Belon 
and Rondelet, whose well-illustrated catalogues of animals were 
appearing from 1550 onwards, did a good service to comparative 
embryology in figuring the ovoviviparous selachians and viviparous 
cetacea. Gesner belongs to this group. All of them reproduce thin 
versions of Aristotle, when they speak of generation as such, and this 
is what differentiates them from Ulysses Aldrovandus, of whom I 
shall speak presently. Figs. 3 and 4 show Rondelet's pictures of a 
viviparous dolphin and an ovoviviparous selachian. 

But the end of the twilight period was now at hand, for, within 
thirty years after the death of de Gerbi in 1505, four great 
embryologists were born as well as the greatest anatomist of any age, 
Andreas Vesalius (1514), of whom I shall say no more, for he had 
no opportunities for dissecting human embryos, and took hardly 
any interest in foetal development. But in 1522 Ulysses Aldrovandus 
was born, and in the following year Gabriel Fallopius, in 1530 
Julius Caesar Arantius and in 1534 Volcher Goiter. Only three 

SECT. 2] 



more years bring us to the birth of Andreas Laurentius and of 
Hieronymus Fabricius ab Aquapendente, the teacher of William 

The senior member of this group, Ulysses Aldrovandus, was the 
first biologist since Aristotle to open the eggs of hens regularly during 

Fig. 3. A (viviparous) dolphin: from Rondelet's De piscibus marinis of 1554. 

their incubation period, and to describe in detail the appearances 
which he found there. In his Ornithologia, published at Bonn in 1597, 
he set out to describe all the known kinds of birds, discussing in 
turn not only their zoological and physiological characteristics, but 

Fig. 4. An (ovoviviparous) shark: from Rondelet's De piscibus marints of 1554. 

also their significance as presages and for augury, their mystical 
meaning, their use as allegories and for eating, and finally all the 
legends respecting them, Generositas, Temperantia, Liberalitas, aquilae 
one finds. Beginning with the eagle, he proceeds to the vulture, 
the owl, the bat (the only viviparous bird!), the ostrich, the harpy (!), 


the parrot, the crow, and so to the fowl. Side by side with a 
reference to the famous poem of Prudentius {Multi sunt Presbyteri, 
translated by J. M. Neale) about the steeple-cock, we find an 
excellent account of the generation of the chick in the c:gg. The book 
is illustrated sumptuously, but unfortunately there is only one picture 
of embryological interest, namely, a chick in the act of hatching. 

In Aldrovandus' embryology there is much discussion of Aristotle 
and Galen, but traces of an independent spirit abound. Pliny's view 
that the heart was formed in the white is "exploded", and Aldro- 
vandus says that it is formed on the yolk-membrane. He refutes the 
opinion of Galen also that the liver is first formed, in connection 
with which he says, "In order that I might bring to an end this 
controversy between the philosophers and the physicians I followed 
with the keenest curiosity and diligence the incubation of 22 hen's 
eggs, opening one each day; thus I found Aristotle's doctrine to be the 
truest. And because apart from the fact that these matters are most 
worthy of being looked into they provide also the greatest pleasure 
and entertainment I have thought it well to describe them as clearly 
and briefly as possible". 

Aldrovandus also contradicts Albertus, and propounds a new 
theory, namely, that the spiritualia (the organs in the thorax) are 
formed from the seed of the cock {ex maris semine sunt). This seed 
he aflfirms to be present in the egg, and he identifies it with the 
chalazae, thus anticipating Fabricius ab Aquapendente, but not 
going quite so far, and explicitly opposing Gaza, who had said not 
long before that the chalazae were simply congealed water. Aldro- 
vandus' admiration for Aristotle is extreme, and, though he differs 
from him about the chalazae, he defends the Aristotelian opinion 
that the chick was made from the white but nourished from the yolk. 
His argument for this is new, however; it is that, during incubation, 
the latter liquefies but the former hardens; now in all digestion 
liquefaction takes place, and in all growth hardening, therefore, etc. 
This argument is a great deal more cogent than most of those which 
were current between 1550 and 1650. He goes out of his way to 
castigate Albertus for saying that the yolk moves up into the sharp 
point of the egg, for experience assures him that it does not, "as I 
have observed by cutting open an egg after one day's incubation". 
A striking instance of his powers of observation was his description 
of the "egg-tooth" of embryonic birds, a discovery made anew in 


the nineteenth century by Yarrell and Rose. The chick was perfect 
in form, according to him, on the tenth day. 

The peculiarity of Aldrovandus lies in the fact that he incorporated 
so many elements into one book, and was able to produce a collection 
of chapters in which good scientific observation sat at the closest 
quarters with literary allusion and semi-theological homily. So well- 
proportioned a mixture as the Ornithologia is not often found. As a 
final instance three consecutive paragraphs may be mentioned, in 
the first of which he discusses Plutarch's arid problem about the 
priority of egg or hen, next he makes some very reasonable remarks 
about teratology, suggesting that monsters come from yolks which are 
physico-chemically abnormal in some way, while in the third he 
expresses strong scepticism concerning the tale that the basilisk is 
sometimes hatched out from a hen's egg — ''Ego ne jurantibus quidem 
crediderim'\ he says. This last notion is found in the fourteenth- 
century poem of Prudentius alluded to above, and appears again in 
the Miscellaneous Exercitations of Caspar Bartholinus the younger, 
whose second chapter is devoted to showing "That the basilisk 
hatcheth not from the egg of the hen", a conclusion which has been 
amply confirmed in the light of subsequent experience. Bartholinus 
gives a bibliography of this curious legend. 

Aldrovandus and his disciple Volcher Coiter the Frisian, as he 
described himself, were alike in not suffering from the prevailing 
vice of the age, verbosity. Colter's Externarum et Internarum princi- 
palium humajii corporis partium tabulae et exercitationes, which appeared 
at Nuremberg in 1573 — a beautifully printed book — contained a 
brief section entitled De ovorum gallinaceorum generationis primo exordio 
progressuque et pulli gallinacei creationis ordine. His Latin style betrays 
his German origin, for the constructions are very Teutonic, although 
the meaning is always perfectly clear. Coiter says, "In the year 
1564 in the month of May at Bologna, being instigated by that 
excellent professor of philosophy outstanding in varied sciences and 
arts. Doctor Ulysses Aldrovandus, and by other doctors and students, 
I ordered 2 broody fowls to be brought and under each of them 
I caused 23 eggs to be placed, and in the company of these persons 
I opened one every day so that we could see firstly the origin of 
the veins and secondly what organ is first formed in the animal". 
What follows is practically a repetition of the facts available in 
Aristotle, but described with much greater clearness than either 


Aristotle or Aldrovandus had been able to bring to the matter. 
On the third day, he saw the globulus sanguineus which in vitello 
manifeste pulsabat, and so solved his first problem. He decides that 
the first organ to be formed is the heart, and quotes Lactantius' 
experiments. He explains the large size of the eye as due to the fact 
that the most complicated part of the body needs the longest time 
for its manufacture. He correctly describes the various membranes, 
and the faeces subviridies in the intestines at hatching. Once he 
contradicts Aristotle, maintaining that on the tenth day the body as 
a whole is larger than the head, and once he contradicts Albertus, 
denying that any yolk can be found in the stomach at hatching. He 
concludes his tractate by a succinct and clear account of the opinions 
of Aristotle and Hippocrates about embryonic development. His 
importance is that he drew the attention of scientific thinkers to the 
problems arising out of the hen's egg, and assisted in the formation 
of that iconographic phase in embryology which was later to find 
its climax in the plates of Fabricius, and its close in Harvey's Exer- 

Gabriel Fallopius, who belongs to this time, must be mentioned 
as the discoverer of the organs which bear his name, but his services 
to embryology were only indirect. A. Benedictus, who was now 
growing old, and Caesar Cremonius, who was still young, may be 
remembered as the principal upholders of pure Aristotelianism at this 
time. Realdus Columbus also wrote on the embryo. B. Telesius, 
in his De Natura Rerum of 1565, studied the hen's egg and suggested 
that the parts of animals were formed by the pressure of the uterus 
acting as a mould: he was thus the middle term between Galen 
and Buffon. 

Julius Caesar Arantius has already been referred to. His De 
Humano Foetu was an important book, but, though it appeared in 
1564, just at the time when the macro-iconographic school was at 
its height, it dealt with a rather different field and cannot be con- 
sidered as a constituent of that group. He begins by relating that a 
pregnant woman was killed by an accident at Bologna a couple of 
years before, so that he had an opportunity of testing whether the 
opinions about certain points in generation, which he had formed 
on a priori grounds during the previous fifteen years, were true or 
not. In the first place, he found on dissection that the placenta was 
not cotyledonous, and he spoke thus of its formation: "Blood flows 


out from the spongy substance of the uterus and this blood growing 
in bulk forms a soft and fungus-like mass of flesh, rather like the 
substance of the spleen, which adheres to the surface of the uterus 
and transmits to the foetus in proportion as it grows the nourishment 
for it which reaches the uterus in the form of blood and spirits". 
Then, going on to discuss the functions of the jecor uterinae, as 
he calls the placenta (with what justice may be seen by turning to 
Section 8-5), he devotes a chapter to De vasorum umbilicalium origine, 
and, contradicting Hippocrates, Galen, Erasistratus, and Aetius, says 
that the maternal and foetal blood-vessels do not pass into each 
other by a free passage. "This is repugnant to sense", he writes, 
"and as may be seen by ocular inspection, these vessels do not reach 
the inner membrane of the uterus, for the substance of the placenta 
is placed between their ramifications and the proper substance of 
the womb." He was thus the first to maintain that the maternal 
and foetal circulations are separate, but he naturally did not, and 
could not, speak of circulations, since he lived before Harvey. Nor 
could he have satisfactorily proved his point with the means then 
at his command, and, as we shall see, it was to take another century 
before the proof was given. Apart from this valuable contribution 
to embryology, Arantius gave some admirable anatomical descrip- 
tions of the foetal membranes. 

Hieronymus Fabricius ab Aquapendente, the pupil of Fallopius, 
has always been given an important place in the history of embryo- 
logy by those who have written on him. As one comes upon him 
in the process of tracing out that history itself, however, he does 
not take such a high place. With the statement, for instance, that 
"Fabricius carried embryology far beyond where Goiter had left 
it and elevated it at one bound into an independent science" I 
find that I cannot agree. Embryologists who called themselves 
that and nothing else did not appear till the end of the eighteenth 
century, and it seems to me doubtful whether the anatomical ad- 
vances in embryology made by Fabricius are not counterbalanced 
by the erroneous theories which he invented at the same time. His 
De Formatione Ovi et Pulli pennatorum, and his De Formato Foetu of 1604 
show far more scholasticism and mere argumentativeness than is to 
be found in Goiter, and are remarkable for their bulk. Fabricius 
seems to have had a genius for exsuccous and formal discussions. He 
spends much time, for example, in taking up the problem of whether 



the yolk of the hen's egg is more earthy than the white, and looking 
at it from all possible angles. He disagrees at last with Aristotle 
and decides that the white is the more earthy. Bones, he says, are 
white, but also very earthy. The albumen is colder, stickier, and 
heavier than the yolk, "sequitur, terrestrius esse^\ And this particular 
example is the more flagrant because the actual matter of it is 
fundamentally physico-chemical. But, in addition, he introduced a 
number of grave errors and misleading theories into embryology, so 
that subsequently Harvey had to spend a large part of his time 
refuting them. Fabricius was, indeed, a good comparative anatomist, 
and it is upon that ground that he deserves praise: his plates, some 
of which are reproduced herewith, were far better than anything 
before and for a long time afterwards. He dissected embryos of man, 
rabbit, guinea-pig, mouse, dog, cat, sheep, pig, horse, ox, goat, deer, 
dogfish, and viper, a comparative study which had certainly never 
been made previously. 

In his first tractate he begins by dealing with a question not unlike 
that of how the sardines got into the tin, i.e. how the contents got 
into the hard-shelled egg. He rejects Aristotle's idea that the egg 
is formed in the oviduct by a kind of umbilicus, and ascribes its 
growth there to transudation through the blood-vessels. He marks 
a definite advance upon Aristotle when he says that silkworms and 
other insects are born into their larval state from an egg, though he 
still terms the chrysalis an egg, and therefore holds that they are 
generated twice. Then follows his discussion of what part of the egg 
the chick comes from. The chalazae, he says, are not semen, for the 
semen is not present at all in the fertilised egg. His argument sounds 
peculiar when he says that both the white and yolk of the egg are 
the food of the embryo, for neither of them is absent at the end of 
incubation, therefore neither of them is its material. Hippocrates 
had said, "^ex luteo gigni, ex albo nutriri''; Aristotle had said, "ex 
albo fieri, ex luteo nutrirV\ The latter was the view generally held 
in the sixteenth century, as may be gathered from Ambrosius 
Calepinus' dictionary, Scaliger's Commentary on Aristotle, and the 
treatise on the soul of Johannes Grammaticus. 

Fabricius now says both nourish, neither makes. This distinction 
between food and building-materials seems to us unnecessary, but 
it had a great influence on later thought. Fabricius devotes much 
time to proving, as he thinks, that albumen and white are of the 




same nature, and adduces the fact that "in cooking the white hardens 
first, whether the egg be boiled or poached, but the yolk hardens 
also if the heat is more", comparing the heat of the kitchen to the 
innate heat of the chick. "But you will say", he goes on, "if the 
albumen and the yolk are the food of the chick in the egg, what 
then must we decide the material of the chick to be, since we have 
already said that the semen is not present in the eggs. You will 
find this material from an enumeration of the parts of the egg — there 
remains only the shell, the two membranes, and the chalazae; — 
nobody will assign the membranes or the shell as the material of 
the chick, therefore the chalazae alone are the fitting substance out 
of which it can be made." Having discovered this truth by the 
infallible processes of logic, Fabricius brings all kinds of arguments 
forward to support it; he adduces the three nodes in the chalazae 
as the precursors of brain, heart, and liver; tadpoles, he thinks, 
resemble significantly the chalazae, being "armless legless spines". 
The eyes are transparent, so are the chalazae, therefore the latter 
must give rise to the former. The liver is formed as soon as the heart 
but is practically invisible as it does not palpitate. One of his most 
gratuitous errors was the suggestion, now newly introduced, that the 
heart (and other organs) of the foetus has no proper function, no 
munus publicum, but beats only in order to preserve its own life. 
Then there is a considerable section called De Ovorum utilitatibus, 
which almost does for the hen's egg what Galen's De Usu Partium 
did for the human body, and in which such questions as Why 
the shell is hard and porous? and Why there are any membranes 
in the egg? are taken up and answered with an elaborate display 
of common sense. The influence of Galen is perceptible in a passage 
about a liver-like substance being formed if blood is freshly shed into 
hot water, in the usual terminology of formative faculties, and in the 
division of fleshes into white and red, though the former is not 
specifically derived fi"om the semen nor the latter from the menstrual 
blood. The human placenta is described as cotyledonous, and need- 
less confusion is caused by the doctrine that the "liquors, humours, 
or rather, excrements, around the foetus, are two in number, sweat 
and urine, the former in the amnios, the latter in the allantois". 
But the drawings and illustrations of Fabricius' work are beautiful 
and accurate — so much so, indeed, that it will always remain 
a mystery how the man who figured the early stages of the 


development of the chick as Fabricius did, showing the blood- 
vessels radiating from the minute heart, should have been able 
to propound the thesis that the chalazae were the material of the 

The other biologist to whom Harvey was most indebted was 
Andreas Laurentius of Montpellier, whose Historia Anatomica (printed 
with his other works in 1628) contained a whole book (viii) devoted 
to embryology, but which presents us with nothing except a com- 
mentary on Hippocrates and Aristotle. The only evidences of life 
are furnished by two polemics, one of which was against Simon 
Petreus of Paris, who had propounded some new views about the 
foetal circulation. Laurentius gave also a table showing the changes 
which occur in the heart and lungs of the foetus at birth. 

It was about this time that the embryological observations of that 
many-sided genius, Hieronymus Cardanus, began to attract atten- 
tion. His main thesis was that the limbs of the embryo were alone 
derived from the yolk, while the rest of the body came from the 
white. This was a well-meant attempt to mediate between the two 
traditions headed respectively by Aristotle and Hippocrates, but the 
arguments in support of it were not even remarkable for ingenuity. 
Constantinus Varolius treated of the formation of the embryo in a 
book which appeared in 1591, but very inadequately. He had 
certainly opened hen's eggs, and describes the fourth-day embryo 
as forma minimi faseoli. But nearly every one of his marginal 
headings begins with the word Cur, and this tells its own story, 
for the didactic style rarely hides genuine works of research. Johannes 
Fernelius, a rather earlier worker, in his De Hominis Procreatione fol- 
lowed Aristotle and Galen in nearly all particulars, and made no 
real contribution to embryology. On its practical obstetrical side, 
the sixteenth century produced some remarkable compilations of 
ancient gynaecological writings. The first of these was that of Caspar 
Wolf, which was published at Ziirich in 1566, and, after having 
been enlarged by Caspar Bauhin in 1586, subsequently formed the 
backbone of the most important and famous one, namely, that of 
Israel Spach (Strassburg, 1597). Although these composite text- 
books represented no real embryological progress, they yet showed 
that great interest in development was alive, an interest which, 
though doubtless utilitarian in its origin, could hardly fail to lead 
to advances of a theoretical nature. (See Fig. 5.) 

Fig. 5. Illustration from W. H. Ryff's Anatomia of 1541. 


The obstetrical literature intended for midwives is also of great 
interest. It was about this time that the first popular guides to their 
subject began to appear, founded not upon mere superstition and 
the remnants of ancient knowledge derived in roundabout fashion 
through Syriac and Arabic, but either upon a careful study of Galen 
and Aristotle, or upon the results of dissections and living speculation. 
The principal representative of the former class is that of Jacob 
Rueff, which appeared in 1554 and was called De Conceptu et Genera- 
tione Hominis. Although written in Latin, it was evidently a popular 
work, for the illustrations given in it are such as would naturally 
be incorporated in such a book. It is the illustrations which give it 
its importance, and I reproduce them in Fig. 6. I think they show 
very clearly what the general ideas were at this period about mam- 
malian embryology, and thus afford us a precious insight into what 
was in the minds of such writers as Riolanus the elder, Mercurialis, 
Saxonia, Rondeletius, Venusti, Holler and Vallesius. There are many 
points which their expositions of foetal growth and development leave 
vague, and without Rueff it would be difficult or impossible to picture 
in what manner they imagined it to go on. Rueff 's text follows Galen 
and Aristotle with fidelity, as does theirs — with the exception of a few 
minor ideas not quite consonant with this. 

In (a) of Fig. 6 Rueff portrays the mixture of semen and menstrual 
blood in the womb, or, as he loosely refers to it, of both seeds, 
coagulating into a pink egg-shaped mass surrounded with a fine 
pellicle, {b) shows the same mass in the uterus and wrapped round 
with the three coats, amnion, chorion, and allantois — a lamentable 
but interesting misrepresentation of the facts. Then in {c) it is shown 
that upon the surface of the yolk-like mass of semen and blood 
appear "three tiny white points not unlike coagulated milk", these 
being the first origins of the liver, the heart, and the brain. Next {d) 
shows the first blood-vessels springing from the heart, four in number, 
and distributing themselves over the surface of the mass. It is plain 
that Rueff must either have opened hen's eggs himself and seen the 
early growth of the blastoderm or have been told about it by some 
observer such as Goiter or Aldrovandus. He could not have copied 
his pseudo-blastoderm pictures from their works, for in 1554 none 
of them had appeared, and, as far as I know, there were no similar 
illustrations in existence at that time. 

After this point the pictures grow even more fanciful, and, in (^), 

Fig. 6. Illustrations from Jacob Rueff's De Conceptu et Generatione Hominis of 1554 
(arranged by Singer) showing the Aristotelian coagulum of blood and seed in the uterus. 


the first outline of the cranium is seen taking shape in the upper 
part of the "egg". In (/) the blood-vessels have suddenly assumed 
the outline of a human being, and in (g) the finished product is seen. 
Rueff gives what seems to be a mnemonic in hexameters : 

iniectum semen, sex primis certe diebus 
est quasi lac : reliquisque novem sit sanguis ; at inde 
consolidat duodena dies; bis nona deinceps 
effigiat; tempusque sequens producit ad ortum 
talis enim praedicto tempore figura consit. 

Rueff gives some excellent diagrams of the foetus in utero with 
relation to the rest of the body, and the various positions which are 
familiar to obstetricians. His teratology is less happy, for he attri- 
butes the production of monsters to the direct action of God, though 
he does venture upon a few speculations concerning "corrupt seed". 
But his principal significance for this history is that, in his picture 
of the yolk-like mass of mixed semen and blood and the pseudo- 
blastoderm upon it, he throws a good light on the conceptions of 
the time. 

Rueff 's book was subsequently translated into English, and had 
many editions as The Expert Midwife. 

The principal representative of the second class of popular books 
of this period is that of Euch. Rhodion, or Rosslein, which was 
translated into English, and published as his own work, by Thomas 
Raynold, " physition ", in 1 545, under the title of The Byrth ofMankynde 
otherwyse named The Woman" s Book (cf. d'Arcy Power). It was the first 
book in the English language to contain copper engravings. They 
were variants of the traditional Soranus-Moschion figures. The 
Rosslein-Raynold book pays less attention to Galenic theory than does 
that of Rueff, and includes much better drawings of actual dissec- 
tions. Another famous obstetrical book was that of Scipio Mercurius; 
for further information here see Spencer. 

The minor embryologists of the sixteenth century included among 
them Ambroise Pare, the founder of modern surgery. His teaching 
on generation involved nothing original, but it seems to have been 
Galenism interpreted by a very intelligent and well-balanced, un- 
speculative mind. The three-bubble theory appears in him very 
clearly; thus, we read, "The seed boileth and fermenteth in the 
womb, and swelleth into three bubbles or bladders" — the brain, the 


liver, and the heart. Fare's illustrations are copied wholesale from 
Vesalius and Rueff, without acknowledgment. The last author to 
take the three-bubble theory quite seriously was A. Deusingius, who 
wrote in 1665, after Harvey. Others who deserve a mention, but 
no more, were Severinus Pinaeus, L. Bonaciolus and Felix Platter. 
None of them made any advance, and the illustrations of the former's 
De Virginitatibus notis graviditate et partu were almost ludicrous. 

Hieronymus Capivaccius, F. Licetus, J. Costaeus and V. Cardelinus, 
who wrote in 1608, were the last true supporters of the ancient 
theories, such as that the male embryo was twice as hot and developed 
twice as quickly as the female. 



3-1. The Opening Years of the Seventeenth Century 

iEmilius Parisanus, a Venetian, now dealt with embryology in the 
fourth, fifth, and sixth books of his De Subtilitate. They were entitled 
as follows: "(4) Of the principles and first instruments of the soul 
and of innate heat, (5) Of the material of the embryo and of its 
efficient cause, (6) Of the part of the animal body which is first 
made, and of the mode and order of procreation". Parisanus is 
very wordy, but he has the merit of giving many quotations from 
the lesser known authors, and providing (as a rule) accurate refer- 
ences. He held that the spleen was formed in all development before 
the heart, and that neither heart nor lungs moved in utero. With 
regard to the controversy over the function of white and yolk, he 
was in agreement with Fabricius, but he firmly opposed the view 
that the chalazae were the first material of the chick, as much, it 
must be confessed, because of the opinion of Aristotle as from his 
own observation. Nevertheless, his own observations were note- 
worthy, and he will always be remembered for his discovery of the 
fact that the heart of the chick begins to beat some time before any 
red blood appears in it. 

Parisanus was the last of the macro-iconographic group of sixteenth- 
century embryologists. Their labours established the fundamental 
morphological facts about the developing embryo; the first great 
step in the history of embryology. But there were numerous errors 
in their work, and Harvey, who occupies a terminal or boundary 
position, was destined to correct them. He marks the transition from 
the static to the dynamic conception of embryology, from the study 
of the embryo as a changing succession of shapes, to the study of it 
as a causally governed organisation of an initial physical complexity, 
in a word, from Goiter and Fabricius to Descartes and Mayow. 
Iconography did not die : on the contrary, the improvement of the 
microscope gave it new life, and the micro-iconographic school 
emerged with its principal glory, Malpighi. 


Harvey sums up the work of the macro-iconographic period in the 
historical introduction contained in Ex. xiv of his De Generatione 
Animalium. I give it in full in the beautiful seventeenth century 
English into which Harvey's Latin was translated under his guidance 
by the physician, Martin Llewellyn, 

"We have already discovered the Formation, and Generation of 
the Egge; it remains that we now deliver our Observations, con- 
cerning the Procreation of the Chicken out of the Egge. An under- 
taking equally difficult, usefull, and pleasant as the former. For 
Nature's Rudiments and Attempts are involved in obscurity and 
deep night, and so perplext with subtilties, that they delude the most 
piercing wit, as well as the sharpest eye. Nor can we easier discover 
the secret recesses, and dark principles of Generation than the method 
of the fabrick and composure of the whole world. In this reciprocal 
interchange of Generation and Corruption consists the ^Eternity 
and Duration of mortal creatures. And as the Rising and Setting 
of the Sun, doth by continued revolutions complete and perfect 
Time; so doth the alternative vicissitude of Individuums, by a 
constant repetition of the same species, perpetuate the continuance 
of fading things. 

"Those Authors which have delivered any thing touching this 
subject, do for the most part tread a several path, for having their 
Judgements prepossessed with their own private opinions, they pro- 
ceed to erect and fashion principles proportionable to them. 

"Aristotle of old, and Hieronymus Fabricius of late, have written 
so accurately concerning the Formation and Generation of the Foetus 
out of the Egge, that they seem to have left little to the industry 
of Posterity, And yet Ulysses Aldrovandus hath undertaken the 
description of the Pullulation or Formation of the chicken out of the 
Egge, out of his own Observations ; wherein he seems rather to have 
directed and guided his thoughts by the Authority of Aristotle, than 
by his own experience. 

"For Volcherus Goiter, living at Bononia at the same time did 
by the advice of the said Aldrovandus (whom he calls Tutor) dayly 
employ himself in the opening of Egges sat upon by the Hen, and 
hath discovered many things truer than Aldrovandus himself, of 
which he also could not be ignorant. Likewise iEmilius Parisanus 
(a Venetian Doctor) despising other mens opinions hath fancied A 
new procreation of the Chicken out of the Egge. 


"But because somethings, (according to our experience) and those 
of great moment and consequence, are much otherwise than hath 
been yet delivered, I shall declare to you what dayly progress is made 
in the egge, and what parts are altered, especially about the first 
dayes of Incubation; at which time all things are most intricate, 
confused, and hard to observe, and about which authors do chiefly 
stickle for their own observations, which they accomodate rather to 
their own preconceived perswasions (which they have entertained 
concerning the Material and Efficient Causes of the generation of 
Animals) than to truth herself. 

"Aldrovandus, partaking of the same error with Aristotle, saith 
(which none but a blind man can subscribe to) that the Yolk doth 
in the first dayes, arise to the Acute Angle of the Egge ; and thinks 
the Grandines to be the Seed of the Cock; and that the Pullus is 
framed out of them, but nourished as well by the yolk as the white ; 
which is clean contrary to Aristotle's opinion, who conceived the 
Grandines to conduce nothing to the fecundity of the egge. Volcherus 
Goiter delivers truer things, and more consonant to Autopsie, yet his 
three Globuli are meer fables. Nor did he rightly consider the 
principle from whence the Foetus is derived in the Egg. Hieronymus 
Fabricius indeed contends, that the Grandines are not the seed of 
the cock, and yet he will have the body of the Chicken to be framed 
out of them (as out of its first matter) being made fruitful by the seed 
of the cock. He likewise saw the Original of the Chicken in the Egge; 
namely the Macula, or Cicatricula annexed to the membrane of the 
Yolke but conceived it to be onely a Relique of the stalk broken off, 
and an in-firmity of blemish onely of the Egge, and not a principle 
part of it. Parisanus hath plentifully confuted Fabricius his opinion 
concerning the Chalazae or Grandines, and yet himself is evidently 
at a loss in some certaine circles and points of the Principle parts 
of the Foetus (namely the Liver and the Heart) and seems to have 
observed a Principium or first Principle of the Foetus, but not to 
have known which it was, in that he saith, that the Punctum Album 
in the Middle of the Circles is the Cocks Seed out of which the Chicken 
is made. So that it comes to pass that while each of them desire to 
reduce the manner of the Formation of the Chicken out of the Egge 
to their own opinions they are all wide from the mark." 

Before discussing how Harvey put them right, however, there are 
a number of other matters to be mentioned. Parisanus' work was 


published in 1623, and twenty-five years were to elapse before 
Harvey's Exercitations were to be put before the learned world by 
George Ent. In that time not a few events of importance for the 
history of embryology took place. 

It will be convenient to speak first of Adrianus Spigelius, whose 
De Formato Foetu appeared in 1 63 1 . In this book the plates of the 
gravid uterus which had been prepared some years before for Julius 
Casserius were now published. They had more influence than 
Spigelius' text, perhaps, in contributing to the permanent fame of 
his book. 

He gives for the most part straightforward anatomical descriptions, 
but he returns to the notion of a cotyledonous placenta in man, and 
he combats Arantius' opinions about the placenta. Arantius had said 
that the function of the jecor uterinae was to purify the blood- 
supply to the foetus, a thoroughly modern idea, but Spigelius opposes 
this on two grounds, firstly, because the foetus has its own organs 
for purifying blood, and secondly, because, if Arantius was right, 
the placenta would always be as red as blood, but this is not the case 
in such animals as the sheep. Spigelius himself thought that the 
placenta was for the purpose of preventing severe loss of blood at 
birth, as would be the case if the embryo was joined to the mother 
with only one big vessel and not a great many little ones. 

However, Spigelius upholds the view, taken by Rufus of Ephesus 
and by Vesalius, that the allantois contains the foetal urine, which 
has to be separated from the amniotic liquid in which the embryo 
is, because it would corrode the embryonic skin [ne cuti tenellae 
aliquod damnum urinae acrimonia inferret). This passage is interesting, 
as showing biochemical rudiments. The first discussion of the 
vernix caseosa, or sordes, as he calls it, appears in Spigelius, who, 
however, hazards no guess as to its nature. He is happy in his 
refutation of Laurentius, who had affirmed that the foetal heart did 
not beat in utero, and he shows some advance on all previous writers 
save Arantius in declaring that the umbilical vessels take vital spirits 
away from the foetal heart, not exclusively to it. He gave, moreover, 
the first denial of the presence of a nerve in the umbilical cord, and also 
made the first observation of the occurrence of milk in foetal breasts 
at birth (for the endocrinological explanation of this see Section 15). 
Finally, he abolished at last the notion that the meconium in the 
foetal intestines argued eating in utero on the part of the embryo. 


Riolanus the younger, the correspondent and almost exactly the 
contemporary of Harvey, was Professor in Paris and published his 
Anthropographia in 1618. As he was a keen advocate of the ancient 
views, his section on the formation of the foetus has little importance. 
Yet it contains the first known instance of the use of the lens in embryo- 
logy, the germ of that powerful instrument which was to lead in 
due course to so many discoveries. "In aborted embryos", said 
Riolanus, "the structure is damaged and can often not be properly 
seen, even when you make use of lenses [conspicilid] which make 
objects so much bigger and more complicated than they ordinarily 

The De Formatrice Foetus of Thomas Fienus, Professor at Louvain 
and a friend of Gassendi, published in 1620, is interesting because 
it is the middle term between Aristotle and Driesch. As the title- 
page informs us, he sets out to demonstrate that the rational soul is 
infused into the human embryo on the third day after conception. 
This by itself would not be very attractive, but the most cursory 
inspection shows that Fienus' interests were not at all theological. 
He divides the book up into seven main questions, (i) What is the 
efficient cause of embryogeny? He concludes that it is neither God, 
nor Intelligence, nor anima mundi (influence of Neo-platonism here 
as on Galileo). (2) Is it in the uterus or in the seed? In the latter, 
says Fienus, adding a list of authorities who agree with this view — 
Haly-Abbas, Gaietanus, Zonzinas, Turisanus, Fernelius, Vallesius, 
Peramatus, Saxonia, Carrerius, Zegarra, Mercurialis, Massaria, and 
Archangelus, ^' solus Fabio Pacio utero imprudenter adscribit'' (!). (3) Is 
it heat? Fienus nearly decided that it was, and, if he had done 
so, would have shown a modern mind, but no, he gave his 
opinion against it, saying, "the process (of development) is so divine 
and wonderful that it would be ridiculous to ascribe it to heat, a 
mere naked and simple quality". After weighing various other 
alternatives in questions (4), (5) and (6), he asks whether it is 
^'^ anima seminis post conceptum adveniens'' (7), and concludes that it is. 
It is here that he becomes really interesting, for he quotes with 
approval certain writers, e.g. Alexander Aphrodisias [Organicum corpus 
esse organicum ab anima et anima praeexistere organizationi) , Themistius 
{Anima fabricatur architecturaque sibi domicilium et accommodatum instru- 
mentum) and Marsilio Ficino in his commentary on Plato's Timaeus 
[Priusquam adultum sit corpus, anima tota in illius fabrica occupatur), and 


then maintains with them that the soul is the principle which 
organises the body from within, arranging an organ for each of 
its faculties and preparing a residence for itself, not merely allowing 
itself to be breathed into a being which has already organised 
itself "The conformation of the foetus is a vital, not a natural, 
action", he says. He develops this idea in the remainder of the 
book; according to him, the seed first coagulates the menstrual 
blood into an amorphous cake, taking three days to do so, after 
which, the rational (not vegetative or sensitive) soul (entelechy), 
which has entered the uterus with the seed, finding a suitable 
mass of shapeless material, enters into it and begins to give it a 
shape. Fienus was attacked by several writers, and published a 
defence of his views. 

Later writers on the same subject included Fidelis, Teichmeyer, 
Albertus, de Reies, Torreblanca and de Mendoza. The Spanish 
influence here is perhaps significant. Hieronymus Florentinus, who 
adopted the same standpoint as Fienus in 1658 was forced to recant it. 

In 1625 Joseph de Aromatari, a Venetian, included in his epistle 
on plants the first definite statement of the preformationist theory 
since Seneca, but he did not develop the idea. He had noted that 
in bulbs and some seeds the rudiments of many parts of the adult 
plant can be seen even without glass or microscope, and this led him 
to suggest that probably in all animals as well as plants a similar 
thing was true. "And as for the eggs of fowls", he said, "I think the 
embryo is already roughly sketched out in the egg before being formed 
at all by the hen [quod attinet ad ova gallinarum, existimamus quidem 
pullum in ovo delineatum esse, antequam formatur a gallina].'' This sug- 
gestion did not begin to bear its malignant fruits till the time of 
Swammerdam and Malpighi. 

Johannes Sinibaldi's Geneanthropia might be mentioned as belonging 
to this time. It was a compilation of facts relating to the generation 
of man, but it expressly excluded from its field any discussion of the 
embryo. It is no more important for our subject than the queer 
Ovi Encomium of Erycius Puteanus, another of Gassendi's friends, which 
has already been referred to (p. 8). 

3-2. Kenelm Digby and Nathaniel Highmore 

Much more significant was the controversy between Sir Kenelm 
Digby and Nathaniel Highmore. In 1644, Sir Kenelm, whose in- 


triguing personality will be sufficiently familiar to anyone even slightly 
acquainted with seventeenth-century England, and whose biographic 
details may be found in John Aubrey, published a work with the 
following title: Two treatises, in the one of which, The Nature of Bodies, 
in the other, The Nature of Man's Soule is looked into, in way of discovery 
of the Immortality of Reasonable Soules. It was inscribed in a charming 
dedication to his son, and consisted, in brief, of a survey of the whole 
realms of metaphysics, physics, and biology from a very individual 
point of view. 

One of Sir Kenelm's principal objects in writing was apparently 
to attack the old terminology of " qualities " in physics and "faculties " 
in biology. To say, as contemporary reasoning did, that bodies were 
red or blue because they possessed a quality of redness or blueness 
which caused them to appear red or blue to us, or again, to say that 
the heart beat because it was informed by a sphygmic faculty, or, 
to take the famous example, that opium sent people to sleep because 
it contained in it a dormitive virtue, appeared mere nonsense and 
word-spinning to Digby, "the last refuge of ignorant men, who not 
knowing what to say, and yet presuming to say something, do often 
fall upon such expressions". 

Digby, like Galileo and Hobbes, wished to explain all phenomena 
by reference to two "virtues" only, those of rarity and density, 
"working by means oflocall Motion". Chapters twenty-three, twenty- 
four, and twenty-five contain his opinions and experiments in embryo- 
logy. He begins by opening the question of epigenesis or preforma- 
tion, practically for the first time since Albert the Great. "Our main 
question shall be", he says, "whether they be framed entirely at 
once, or successively, one part after another? And if this latter way, 
which part first?" He declares for epigenesis, but after a manner 
of his own, refuting "the opinion of those who hold that everything 
containeth formally all things". "Why should not the parts be made 
in generation", he asks, "of a matter like to that which maketh them 
in nutrition? If they be augmented by one kind of juyce that after 
severall changes turneth at the length into flesh and bone; and into 
every sort of mixed body or similar part whereof the sensitive creature 
is compounded, and that joyneth itself to what it findeth there already 
made, why should not the same juyce with the same progresse of 
heat and moisture, and other due temperaments, be converted at 
the first into flesh and bone though none be formerly there to joyn 


it self unto?" He gives a clearly deterministic account of develop- 
ment. "Take a bean, or any other seed and put it in the earth, and 
let water fall upon it; can it then choose but that the bean must swell? 
The bean swelling, can it choose but break the skin? The skin 
broken, can it choose (by reason of the heat that is in it) but push 
out more matter, and do that action which we may call germinating? 
Can these germs choose but pierce the earth in small strings, as they 
are able to make their way? . . . Thus by drawing the thrid carefully 
along through your fingers, and staying at every knot to examine 
how it is tyed ; you see that this difficult progresse of the generation 
of living creatures is obvious enough to be comprehended and the 
steps of it set down; if one would but take the paines and afford 
the time that is necessary to note diligently all the circumstances in 
every change of it. . . . Now if all this orderly succession of mutations 
be necessarily made in a bean, by force of sundry circumstances and 
externall accidents ; why may it not be conceived that the like is also 
done in sensible creatures, but in a more perfect manner, they being 
perfecter substances? Surely the progresse we have set down is much 
more reasonable than to conceive that in the seed of the male there 
is already in act, the substance of flesh, bone, sinews, and veins, and 
the rest of those severall similar parts which are found in the body 
of an animall, and that they are but extended to their due magnitude 
by the humidity drawn from the mother, without receiving any 
substantiall mutation from what they were originally in the seed. 
Let us then confidently conclude, that all generation is made of a 
fitting, but remote, homogeneall compounded substance upon which 
outward Agents, working in the due course of Nature, do change it 
into another substance, quite different from the first, and do make it 
lesse homogeneall than the first was. And other circumstances and 
agents do change this second into a third, that third, into a fourth; 
and so onwards, by successive mutations that still make every new 
thing become lesse homogeneall than the former was, according to 
the nature of heat, mingling more and more different bodies together, 
untill that substance bee produced which we consider the period of 
all these mutations." This passage is indeed admirable, and well 
expresses the most modern conception of embryonic development, 
that of the ovum as a physico-chemical system, containing within 
itself only to a slight and varying degree any localisation answering 
to the localisation of the adult, and ready to change itself, once the 



appropriate stimulus has been received, into the completed embryo 
by the actions and reactions of its own constituents on the one hand 
and the influence of the fitting factors of the environment upon the 
other. Digby has not received his due in the past; he stands to 
embryology as an exact science, much in the same relationship as 
Bacon to science as a whole. 

"Generation is not made", he says, "by aggregation of like parts 
to presupposed like ones; nor by a specificall worker within; but by 
the compounding of a seminary matter with the juice which accrueth 
to it from without and with the steams of circumstant bodies, which 
by an ordinary course of nature are regularly imbibed in it by degrees 
and which at every degree doe change it into a different thing ..." (see 
p. 317). "Therefore to satisfie ourselves herein, it were well we made 
our remarks on some creatures that might be continually in our power 
to observe in them the course of nature every day and hour. Sir lohn 
Heydon, the Lieutenant of his Majesties Ordnance (that generous 
and knowing Gentleman, and consummate Souldier both in theory 
and practice) was the first that instructed me how to do this, by 
means of a furnace so made as to imitate the warmth of a sitting hen. 
In which you may lay severall eggs to hatch, and by breaking them 
at severall ages you may distinctly observe every hourly mutation 
in them if you please." Sir Kenelm then goes on to describe the 
events that take place in the incubating egg, which he does very 
accurately, though briefly. In vivipara, he says, the like experiments 
have been made, and the like conclusions come to by "that learned 
and exact searcher into nature. Doctor Harvey" — these he must 
have learnt of by word of mouth, for Harvey's book had not at that 
time been published. As regards heredity, he adopts a pure theory 
of pangenesis, and has more to say about it than any other writer 
of his time. He is sure that the heart is first formed both in ovipara 
and vivipara, "whose motion and manner of working evidently ap- 
pears in the twinckling of the first red spot (which is the first change) 
in the egge". 

Sir Kenelm Digby not only anticipated the outlook of the physico- 
chemical embryologist, but he also foreshadowed with considerable 
accuracy Wilhelm Roux's definition of interim embryological laws. 
"Out of our short survey", he says, "of which (anserable to our weak 
talents, and slender experience) I perswade myselfe it appeareth 
evidently enough that to effect this worke of generation there needeth 


not to be supposed a forming virtue or Vis Formatrix of an unknown 
power and operation, as those that consider things suddenly and in 
grosse do use to put. Yet in discourse, for conveniency and shortnesse 
of expression we shall not quite banish that terme from all commerce 
with us; so that what we mean by it be rightly understood, which is 
the complex assemblement, or chain of all the causes, that concur 
to produce this effect, as they are set on foot to this end by the great 
Architect and Moderatour of them, God Almighty, whose instrument 
Nature is : that is, the same thing, or rather the same things so ordered 
as we have declared, but expressed and comprized under another 
name." Thus Sir Kenelm admits that it is allowable to speak of the 
"complex assemblement" of causes, as if it were one formative virtue, 
and this corresponds to Roux's "secondary components" or interim 
embryological laws. But that the portmanteau generalisations can 
be resolved into ultimate physico-chemical processes, Digby both 
believes and spends two entire chapters in trying to show. Digby 
has been one of the two seventeenth-century Englishmen most under- 
estimated in the history of biology, but his place is in reality a very 
high one. How far he was in advance of his time may be gauged 
from the work of his contemporary Sperlingen, whose book of 1641 
was thoroughly scholastic and retrograde. 

His Treatise on Bodies evoked several answers. Undoubtedly the 
most interesting from the progressive side was that of Nathaniel 
Highmore, who will always be well remembered in embryological 
history. Highmore's The History of Generation came out in 1651, so 
that Harvey must have known of it, and it is one of the puzzles of 
this period why Harvey did not make any mention of it in his work, 
especially as J. D. Horst in a letter to Harvey refers to Highmore as his 
pupil. Harvey replying in 1655 said he had not seen Highmore for 
seven years. Highmore's title-page expressly states that his book is 
an answer to the opinions of Sir Kenelm Digby. But before dis- 
cussing in what the answer consisted, we may look at the plate which 
is bound in immediately after the dedication (to Robert Boyle). 
It is interesting in that it shows again the idea initiated by Leonardo, 
namely, that all growing things, plants as well as animals, have an 
umbilical cord, and in that the drawings of the chick embryos and 
eggs are more quaint than accurate (Plate VI). 

Highmore first describes the Aristotelian doctrine of form and 
matter, and then censures both it and the extensions of it with their 


"qualities", etc., much as Digby himself had done. "Some of our 
later philosophers have showed us that those forms w'^*^ they thought 
and taught to bee but potentially in the matter, are there actually 
subsisting though till they have acquired fitting organs, they manifest 
not themselves. And that the effects which were done before their 
manifestation (as the forming and fashioning of the parts wherein 
they are to operate) can rise from nothing else than from the Soul 
itselfe. This likewise I shall leave to the Readers enquiry, and shall 
follow that other way of introducing Forms, and Generation of 
creatures (as well animals as vegetables) which gives Fortune and 
Chance the preheminency in that work." He then describes Sir 
Kenelm's opinions, quoting from him in detail, and dissents from 
them mainly on the ground that they do not sufficiently account 
for embryogeny, as it were, from a technical point of view. That they 
subvert the "antique principals of philosophy" does not worry 
Highmore, but in his view their detailed mechanisms do not explain 
the facts, a much more serious drawback. Highmore is himself by 
way of being an Atomist, and it is because embryology was first 
treated by him from an atomistic standpoint that he derives his 
importance. "The blood, that all parts may be irrigated with its 
benigne moisture, is forc'd by several channels to run through every 
region and part of the body; by which meanes every part out of 
that stream selects those atomes which they finde to be cognate to 
themselves. Amongst which the Testicles abstract some spiritual 
atomes belonging to every part, which had they not here been 
anticipated, should have been attracted to those parts, to which 
properly they did belong for nourishment. . . . These particles passing 
through the body of the Testicles, and being in this Athanor cohobated 
and reposited into a tenacious matter, at last passe through infinite 
Meanders through certain vessels, in which it undergoes another 
digestion and pelicanizing." Highmore objects, therefore, more to 
Digby 's theory of pangenesis than to his description of embryogenesis. 
He goes on to give a long description of the development of the chick 
in the egg, mentioning in passing that the albumen corresponds to 
the semen and the blood of vivipara and the yolk to their milk. 
"Fabritius, who hath taken a great deal of pains in dissections. . . 
supposes the chick to be formed from the chalazae, that part which 
by our Women is called the treddle. But this likewise is false, for 
then every egge should produce 2 chickens, there being one treddle 


l^: j: 


9 pp ^^^E 


■^ ^ 


0y: 6^^- 

0a: ^f 

Tat-. 1^ 

(P^: 6. 




at each end of the egg, which serve for no other end than for Hga- 
ments to contain the yolk in an equilibrium, that it might not by 
every moving of the egg be shakt, broke, and confused with the white." 
Highmore was the first to draw attention to the increase of brittleness 
which takes place in the egg-shell during incubation, and he holds 
still to the Epicurean view that the female produces a kind of seed, 
though he thinks that the chick embryo is nourished in the early 
stages by the amniotic liquid. 

Perhaps the most interesting reply to Digby from the traditional 
angle was that of Alexander Ross. In his Philosophicall Touchstone he 
upheld the Galenic view that the liver must be first formed in genera- 
tion, for the nourishment is in the blood and the blood requires a liver 
to make it : ergo, the liver must be the earliest organ. Such arguments 
could dispense with observations. Ross also mentions Digby's sug- 
gestion that the "formative virtue" was only a bundle of natural 
causes, but he claims that the notion was an old one in school- 
philosophy, being included in the phrase causa causae^ causa 

3-3. Thomas Browne and the Beginnings of Chemical Em- 

There are references to embryology in Sir Thomas Browne's 
Pseudodoxia Epidemica, or Inquiries into very many vulgar Tenents and 
commonly received Truths, which was published at this time. The 
twenty-eighth chapter of the third book contains a number of 
difficult problems in the embryology of the period, in most cases 
stated without any solution. "That a chicken is formed out of the 
yolk of the Egg was the opinion of some Ancient Philosophers. 
Whether it be not the nutrient of the Pullet may also be considered ; 
since umbilical vessels are carried into it, since much of the yolk 
remaineth after the chicken is formed, since in a chicken newly 
hatched, the stomack is tincted yellow and the belly full of yelk 
which is drawn at the navel or vessels towards the vent, as may be 
discerned in chickens a day or two before exclusion. Whether the 
chicken be made out of the white, or that be not also its aliment, 
is likewise very questionable, since an umbilical vessel is derived unto 
it, since after the formation and perfect shape of the chicken, much 
of the white remaineth. Whether it be not made out of the grando, 
gallature, germ, or tred of the egg, as Aquapendente informeth us, 


seemed to many of doubt; for at the blunter end it is not discovered 
after the chicken is formed, by this also the white and the yelk are 
continued whereby it may conveniently receive its nutriment from 
them both.. . .But these at last and how in the Cicatricula or little 
pale circle formation first beginneth, how the Grando or tredle, are 
but the poles and establishing particles of the tender membrans 
firmly conserving the floating parts in their proper places, with many 
observables, that ocular Philosopher and singular discloser of truth, 
Dr Harvey hath discovered, in that excellent discourse of generation, 
so strongly erected upon the two great pillars of truth, Experience, 
and Reason. 

"That the sex is discernable from the figure of eggs, or that cocks 
or hens proceed from long or round ones, experiment will easily 
frustrate.. . .Why the hen hatcheth not the egg in her belly? Why 
the egg is thinner at one extream? Why there is some cavity or 
emptiness at the blunter end? Why we open them at that part? 
Why the greater end is first excluded [cf p. 233]? Why some eggs 
are all red, as the Kestrils, some only red at one end, as those of 
kites and buzzards? Why some eggs are not oval but round, as 
those of fishes ? etc. are problems whose decisions would too much 
enlarge this discourse." And elsewhere, "That (saith Aristotle) which 
is not watery and improlifical will not conglaciate; which perhaps 
must not be taken strictly, but in the germ and spirited particles; 
for Eggs, I observe, will freeze, in the albuginous part thereof". 
Again, "They who hold that the egg was before the bird, prevent 
this doubt in many other animals, which also extendeth unto them; 
for birds are nourished by umbilical vessels and the navel is manifest 
sometimes a day or two after exclusion.. . .The same is made out 
in the eggs of snakes, and is not improbable in the generation of 
Porwiggles or Tadpoles, and may also be true in some vermiparous 
exclusions, although (as we have observed in the daily progress of 
some) the whole Magot is little enough to make a fly without any 
part remaining. . . . The vitreous or glassie flegm of white of egg will 
thus extinguish a coal." 

These citations show Sir Thomas to have been more than simply 
the supreme artist in English prose which is his common title to 
remembrance. In picking his way carefully among the doubtful 
points and difficult problems which previous embryologists had pro- 
pounded but not answered, he usually managed to give the right 


answer to each. But in addition to this, he was also an experimentahst, 
he had made both anatomical and physical experiments on eggs, 
and he was prepared to put any disputed point to the test of "ocular 
aspection", if this could be done. His experimental contributions 
to embryology come out more clearly in his Commonplace Books which 
were published by Wilkin in 1836. 

"Runnet beat up with the whites of eggs seems to perform nothing, 
nor will it well incorporate, without so much heat as will harden 
the tgg. . . . Eggs seem to contain within themselves their own 
coagulum, evidenced upon incubation, which makes incrassation of 
parts before very fluid.. . .Rotten eggs will not be made hard by 
incubation or decoction, as being destitute of that spirit or having 
the same vitiated. . . . They will be made hard in oil but not so easily 
in vinegar which by the attenuating quality keeps them longer from 
concoction, for infused in vinegar they lose the shell and grow big 
and much heavier then before. ... In the ovary or second cell of the 
matrix the white comes upon the yolk, and in the later and lower 
part, the shell is made or manifested. Try if the same parts will give 
any coagulation unto milk. Whether will the ovary best?... The 
whites of eggs drenched in saltpeter will shoot forth a long and hairy 
saltpeter and the egg become of a hard substance. Even in the whole 
egg there seems a great nitrosity, for it is very cold and especially 
that which is without a shell (as some are laid by fat hens) or such 
as are found in the egg poke or lowest part of the matrix, if an hen 
be killed a day or two before she layeth. . . . Difference between the 
sperm of frogs and eggs, spawn though long boiled, would not grow 
thick and coagulate. In the eggs of skates or thornbacks the yolk 
coagulates upon long docoction, not the greatest part of the white. . . . 
In spawn of frogs the little black specks will concrete though not the 
other. ... In eggs we observe the white will totally freeze, the yolk, with 
the same degree of cold will grow thick and clammy like the gum of 
trees, but the sperm or tread hold its former body, the white growing 
stiff that is nearest to it." 

The only conclusion that can be drawn from these remarkable 
observations is that it was in the " laboratory " in Sir Thomas' house 
at Norwich that the first experiments in chemical embryology were 
undertaken. His significance in this connection has so far been quite 
overlooked, and it is time to recognise that his originality and genius 
in this field shows itself to be hardly less remarkable than in so many 


others. To have occupied himself with the chemical properties of 
those substances which afford the raw material of development was 
a great step for those times, but it was not until some twenty-five 
years later that Walter Needham carried this new interest into the 
mammalian domain, and made chemical experiments there. 

3-4. William Harvey 

The Latin edition of William Harvey's book on the generation of 
animals appeared in 1651, and the English in 1653. The frontispiece 
of the former which is reproduced as the frontispiece of this book is 
a very noteworthy picture, and derives a special interest from the 
fact that on the egg which Zeus holds in his hands is written, "^x 
ovo omnia'\ — a conception which Harvey is continually expounding 
(see especially the chapter, "That an egg is the common Original 
of all animals"), but which he never puts into epigrammatic form 
in his text, so that the saying, omne vivum ex ovo, often attributed 
to him, is only obliquely his. 

The De Generatione Animalium was written at different times during 
his life, and not collected together for publication until George Ent, 
of the College of Physicians, persuaded Harvey to give it forth about 
1650. As early as 1625 Harvey was studying the phenomena of 
embryology, as is shown among other evidences by a passage in his 
book where he says, "Our late Sovereign King Charles, so soon as 
he was become a man, was wont for Recreation and Health sake, 
to hunt almost every week, especially the Buck and Doe, no Prince 
in Europe having greater store, whether wandring at liberty in the 
Woods and Forrests or inclosed and kept up in Parkes and Chaces. 
In the three summer moneths the Buck and the Stagge being then 
fat and in season were his game, and the Doe and Hind in the 
Autumme and Winter so long as the three seasonable moneths con- 
tinued. Hereupon I had a daily opportunity of dissecting them and 
of making inspection and observation of all their parts, which liberty 
I chiefly made use of in order to the genital parts". Nor was Harvey 
less diligent in examining the generation of ovipara. John Aubrey, 
in his Brief Lives, says, " I first sawe Doctor Harvey at Oxford in 1642 
after Edgehill fight, but I was then too young to be acquainted with 
so great a Doctor. I remember that he came often to Trin. Coll. 
to one George Bathurst, B.D. who kept a hen in his chamber to 


hatch egges, which they did dayly open to discerne the progress 
and way of generation". Aubrey mentions a conversation he had with 
a sow-gelder, a countryman of Httle learning, but much practical 
experience and wisdom, who told him that he had met Dr Harvey, 
who had conversed with him for two or three hours, and "if he had 
been", the man remarked, "as stiff as some of our starched and 
formall doctors, he had known no more than they". Harvey seems 
also to have learnt all he could from the keepers of King Charles' 
forests, as several passages in his book show. Nor was the King's own 
interest lacking. "I saw long since a foetus", he says, "the magnitude 
of a peasecod cut out of the uterus of a doe, which was complete 
in all its members & I showed this pretty spectacle to our late King 
and Queen. It did swim, trim and perfect, in such a kinde of white, 
most transparent and crystalline moysture (as if it had been treasured 
up in some most clear glassie receptacle) about the bignesse of a 
pigeon's Ggge, and was invested with its proper coat." And, again — 
"My Royal Master, whose Physitian I was, was himself much 
delighted in this kinde of curiosity, being many times pleased to be 
an eye-witness, and to assert my new inventions". 

Harvey's book is composed of seventy-two exercitations, which 
may be divided up for convenience into five divisions. In Nos. i 
to 10 he speaks of the anatomy and physiology of the genital organs 
of the fowl, and the manner of production of eggs. Nos. 11 to 13 
and also Nos. 23 and 36 deal with the hen's egg in detail, describing 
its parts and their uses, while in Nos. 14 to 23 the process of the 
"generation of the foetus out of the hen egge'' is described. The 
greater part of the book, comprising Nos. 25 to 62, as well as Nos. 71 
and 72, is theoretical, and treats of the embryological theories held 
by Aristotle on the one hand, and the physicians, following Galen, 
on the other, instead of which it propounds new views upon the 
subject. Finally, Nos. 63 to 70, as well as the two appendices^ or 
"particular discourses", are concerned with embryogenesis in vivi- 
parous animals, especially in hinds and does. 

It will be best to refer to certain details and main points of interest 
in Harvey's discussions, before trying to assess his principal contribu- 
tions to the science as a whole. Harvey is the first, since Aristotle, 
to refer to the "white yolk" of birds. "For between the yolk", he 
says, "which is yet in the cluster and that which is in the midst of 
the eg when it is perfected this is the difference in chief, that though 


the former be yellowish in colour and in appearance, yet its con- 
sistence representeth rather the white, and being sodden, thickeneth 
like it, growing compact and viscous and may be cut into slices. But 
the yolk of a perfect eggc being boiled groweth friable and of a more 
earthy consistence, not thick and glutinous like the white." All of 
Harvey's observations on the formation of the egg in the oviduct 
contained in this chapter are interesting, and may with advantage 
be compared with the studies of Riddle upon the same subject, where 
the chemical explanation will be found for many of Harvey's simple 
observations. Harvey's controversy with Fabricius on the question 
of whether the egg is produced with a hard shell or only acquires 
its external hardness upon standing in the air, which follows im- 
mediately on the above citation, is interesting. "Fabricius seemeth 
to me to be in errour, for though I was never so good at slight of 
hand to surprise an egge in the very laying, and so make discovery 
whether it was soft or hard, yet this I confidently pronounce that the 
shell is compounded within the womb of a substance there at hand 
for the purpose, and that it is framed in the same manner as the 
other parts of the egg are by the plastick faculty, and the rather, 
because I have seen an exceeding small egge which had a shell of 
its own and yet was contained within another egge, greater and 
fairer than it, which egge had a shell too." 

Harvey was the first to note that the white of the hen's egg is 
heterogeneous, in the sense that part of it is much more liquid than 
the rest, and that the more viscous part seems to be contained in an 
exceedingly fine membrane, so that if it is sliced across with a knife, 
its contents will flow out. He also set right the errors of Fabricius, 
Parisanus and others, by showing that the chalazae were neither the 
seed of the cock nor the material out of which the embryo was formed, 
and, most important of all, by demonstrating that the cicatricula 
was the point of origin of the embryo. He denied, as against popular 
belief, that the hen contributed anything to the developing egg but 
heat, "For certain it is that the chicken is constituted by an internal 
principle in the egge, and that there is no accession to a complete 
and perfect egge by the Hennes incubation, but bare cherishing and 
protection; no more than the Hen contributeth to the chickens 
which are now hatched, which is only a friendly heat, and care, by 
which she defendeth them from the cold, and forreign injuries and 
helpeth them to their meat". Whether future work will still affirm 


that nothing is given to the egg by the hen except heat is beginning 
now to be in doubt, if the results of Chattock are correct. 

In the description of the development of the embryo in the hen's 
egg, which remains to this day one of the most accurate, Harvey 
says with regard to the spot on the yolk, which had, of course, been 
seen and mentioned by many previous observers, "And yet I con- 
ceive that no man hitherto hath acknowledged that this Cicatricula 
was to be found in every egge nor that it was the first Principle of 
the Egge". His description of the beginning of the heart, that 
"capering bloody point" or "punctum saliens'\ is too famous to 
need more than a reference. He thought that the amniotic liquid 
was of "mighty use", "For while the embryos swim there, they are 
guarded and skreened from all concussion, contusion, and other out- 
ward injuries, and are also nourished by it". 

Thus he made no advance on the opinion which had for long been 
held, namely, that the amniotic liquid or colliquamentum served 
for sustenance. "I believe", he says, "that this colliquamentum or 
water wherein the foetus swims doth serve for his sustenance and 
that the thinner and purer part of it, being imbibed by the umbilicall 
vessels, does constitute and supply the primo-genital parts, and the 
rest, like Milk, being by suction conveyed into the stomack and there 
concocted or chylified, and afterwards attracted by the orifices of 
the Meseraick Veins doth nourish and enlarge the tender embryo." 
His arguments for this are, ( i ) that swallowing movements take place, 
and (2) that the gut of the chicken is "stuft" with excrement which 
could hardly arise from any other source. He was thus led to divide 
the amniotic liquid into two quite imaginary constituents, a purer 
and "sincerer" part, which could be absorbed straight into the blood 
without chylification, and a creamless milky part which could not 
be treated so simply. 

"About the fourth day", says Harvey, "the egg beginneth to step 
from the life of a plant to that of an animall." "From that to the 
tenth it enjoys a sensitive and moving soul as Animals do, and after 
that, it is compleated by degrees and being adorned with Plumes, 
Bill, Clawes and other furniture, it hastens to get out." These and 
other passages which deal with the forerunner of the theory of re- 
capitulation are interesting, but we have already met essentially the 
same idea in Aristotle. Harvey contributed nothing new to it. The 
first point on which he went definitely wrong was the statement that 


he made that the heart does not pulsate before the appearance of 
the blood. No doubt his lack of microscopical facilities or of the 
desire to use them affords the reason for this error, but it was a very 
unfortunate one, for it was to a large extent upon it that he formulated 
his doctrine "the life is in the blood". For example, he says, "I am 
fully satisfied that the Blood hath a being before any other part of the 
body besides, and is the elder brother to all other parts of the foetus ". 

The yolk, Harvey thought, supplied the place of milk, "and is 
that which is last consumed, for the remainder of it (after the chicken 
is hatched and walks abroad with the Henne) is yet contained in its 
belly". He thus ranged himself with Alcmaeon and Abderhalden. 
All his remarks about the relationships of yolk and white in nutrition 
are worth consideration; in noting, for instance, that the yolk is 
the last to be consumed, he comes very near to anticipating the 
knowledge of the succession of energy-sources which we now possess 
(see Section T"]). "In that Physitians affirme, that the Yolke is the 
hotter part of the ^gg&, and the most nourishing, I conceive that they 
understand it, in relation to us, as it is become our nourishment, 
not as it doth supply more congruous aliment to the chicken in the 
tggt. And this appeares out of our history of the Fabrick of the 
chicken ; which doth first prey upon and devoure the thinner part of 
the white, before the grosser; as it were a more proper diet, and did 
more easily submit to transmutation into the substance of the foetus. 
And therefore the yolke seems to be a remoter and more deferred 
entertainment than the white; for all the white is quite and clean 
spent, before any notable invasion is made upon the yolke." A com- 
parison between these simple facts and our knowledge of embryonic 
nutrition is most interesting (see Section 6-9). 

In connection with Minot's distinction of the periods of embryonic 
growth, it is curious that Harvey says, "And now the foetus moves 
and gently tumbles, and stretcheth out the neck though nothing of 
a brain be yet to be seen, but merely a bright water shut up in a small 
bladder. And now it is a perfect Magot, differing only from those 
kinde of wormes in this, that those when they have their freedom 
crawle up and down and search for their living abroad, but this 
worm constant to his station, and swimming in his own provision, 
draws it in by his Umbilicall Vessels". 

Sometimes Harvey confesses himself puzzled by problems which 
could only be solved by chemical means, yet it does not occur to 


him that this is the case. For instance, he enquires why heat will 
develop a chick out of a good egg but will only make a bad one worse. 
"Give me leave to add something here", he writes, "which I have 
tried often; that I might the better discerne the scituation of the 
foetus and the liquors at the seventeenth day to the very exclusion. 
I have boiled an eggc till it grew hard, and then pilling away the 
shell and freeing the scituation of the chicken, I found both the 
remaining parts of the white, and the two parts of the yolk of the 
same consistence, colour, tast, and other accidents, as any other stale 
egge, thus ordered, is. And upon this Experiment, I did much ponder 
whence it should come to passe that Improlifical eggs should, from 
the adventitious heat of a sitting Henne, putrifie and stink; and yet 
no such inconvenience befall the Prolifical. But both these liquors 
(though there be a Chicken in them too, and he with some pollution 
and excrement) should be found wholesome and incorrupt; for that 
if you eat them in the dark after they are boyled, you cannot dis- 
tinguishe them from egges that are so prepared, which have never 
undergone the hen's incubation." Harvey was never afraid of trying 
such tests on himself; in another place, for example, he says, "Eggs 
after 2 or 3 days incubation, are even then sweeter relished than stale 
ones are, as if the cherishing warmth of the hen did refresh and 
restore them to their primitive excellence and integrity". "And the 
yolke (at 14 days) was as sweet and pleasant as that of a newlaid 
cgge, when it is in like manner boyled to an induration." Another 
matter on which Harvey set Fabricius right was on the question 
whether at hatching the hen helps the chicken out or the chicken 
comes out by itself. The latter was the belief held by Harvey, who 
said of Fabricius' arguments on this point that they were "pleasant 
and elegant, but not well bottomed". 

On the great question of preformation v. epigenesis, Harvey keenly 
argued in favour of the latter view. "There is no part of the future 
foetus actually in the egg, but yet all the parts of it are in it poten- 
tially. ... I have declared that one thing is made out of another two 
several wayes and that as well in artificial as natural productions, 
but especially in the generation of animals. The first is, when one 
thing is made out of another thing that is pre-existent, and thus a 
Bedstead is made out of Timber, and a Statue out of a Rock, where 
the whole matter of the future fabrick was existent and in being, 
before it was reduced into its subsequent shape, or any tittle of the 


designe begun. But the other way is when the matter is both made 
and receiveth its form at the same time. ... So Hkewise in the Genera- 
tion of Animals, some are formed and transfigured out of matter 
already concocted and grown and all the parts are made and dis- 
tinguished together per metamorphosin, by a metamorphosis, so 
that a complete animal is the result of that generation; but some 
again, having one part made before another, are afterwards nourished, 
augmented, and formed out of the same matter, that is, they have 
parts, whereof some are before, and some after, other, and at the 
same time, are both formed, and grow. . . . These we say are made 
per epigenesin, by a post-generation, or after-production, that is 
to say, by degrees, part after part, and this is more properly called 
a Generation, than the former. . . . The perfect animals, which have 
blood, are made by Epigenesis, or superaddition of parts, and do 
grow, and attain their just future or ciKfir} after they are born. . . . An 
animal produced by Epigenesis, attracts, prepares, concocts, and 
applies, the Matter at the same time, and is at the same time formed, 
and augmented.. . .Wherefore Fabricius did erroniously seek after 
the Matter of the chicken (as it were some distinct part of the egg 
which went to the imbodying of the chicken) as though the genera- 
tion of the chicken were effected by a Metamorphosis, or trans- 
figuration of some collected lump or mass, and that all the parts of 
the body, at least the Principall parts, were wrought off at a heat 
or (as himselfe speaks) did arise and were corporated out of the 
same Matter." Nothing could be more plain than Harvey's teaching 
on epigenesis, so that he has precedence over Caspar Wolff on this 

On the relation between growth and differentiation Harvey has 
some valuable things to say. The term "nutrition" he restricted to 
that which replaces existent structures, and the term "augmenta- 
tion" or "increment" to that which contributes something new. That 
process which led to greater diversity of form and complexity of shape 
he called "formation" or "framing". "For though the head of the 
Chicken, and the rest of its Trunck or Corporature (being first of 
a similar constitution) do resemble a Mucus or soft glewey substance; 
out of which afterwards all the parts are framed in their order; yet 
by the same Operatour they are together made and augmented, and 
as the substance resembling glew doth grow, so are the parts dis- 
tinguished. Namely they are generated, altered, and formed at once, 


they are at once similar and dissimilar, and from a small similar is 
a great organ made." Harvey was thus very certain that the processes 
of growth in size and differentiation in shape went on quite con- 
currently, though he had no inkling of changes in the relative rapidity 
of each process. On this point he goes further than Fabricius. 
Fabricius thought that growth was a more or less mechanical process, 
taking its origin from the properties of elementary substances, but 
that differentiation was brought about by some more spiritual or 
subtle activity. "Fabricius", says Harvey, "affirmes amisse, that 
the Immutative Faculty doth operate by the qualities of the elements, 
namely. Heat, Gold, Moisture, and Dryness (as being its instruments) 
but the Formative works without them and after a more divine 
manner; as if (forsooth) she did finish her task with Meditation, 
Choice, and Providence. For had he looked deeper into the thing, 
he would have seen that the Formative as well as the Alterative 
Faculty makes use of Hot, Cold, Moist, and Dry, (as her instruments) 
and would have deprehended as much divinity and skill in Nutrition 
and Immutation as in the operations of the Formative Faculty her 
self." "I say the Concocting and Immutative, the Nutritive and 
Augmenting Faculties (which Fabricius would have to busie them- 
selves only about Hot, Cold, Moist, and Dry, without all knowledge) 
do operate with as much artifice, and as much to a designed end, as 
the Formative faculty, which he affirms to possess the knowledge 
and fore-sight of the future action and use of every particular part 
and organ." Thus although in nearly every respect Harvey makes an 
advance on Fabricius, yet here he is retrograde, for, in the former's 
thought, the growth process at least had struggled towards a deter- 
ministic schema; with Harvey this movement is rigidly suppressed. 
"All things are full of deity" {Jovis omnia plena), said he, "so also in 
the little edifice of a chicken, and all its actions and operations, Digitus 
Dei, the Finger of God, or the God of Nature, doth reveal himself" 

There can be no doubt that Harvey's leanings were vitalistic. In 
the following passage, he argues against both those who wished to 
deduce generation from properties of bodies (like Sir Kenelm Digby) 
and the Atomists ; in other words, against the outlook of those types 
of mind which in later times were to build up biophysics and bio- 
chemistry. Aubrey notes that Harvey was "disdainfull of the chymists 
and undervalued them". 

"It is the usual error of philosophers of these times", says he, "to 


seek the diversity of the causes of parts out of the diversity of the 
matter from whence they should be framed. So Physicians affirm, 
that the different parts of the body are fashioned and nourished by 
the different materials of blood or seed ; namely the softer parts, as 
the flesh, out of a thinner matter, and the more earthy parts as the 
bones, out of grosser and harder. But this error now too much 
received, we have confuted in another place. Nor are they lesse 
deceived who make all things out of Atomes, as Democritus, or out 
of the elements, as Empedocles. As if (forsooth) Generation were 
nothing in the world, but a meer separation, or Collection, or Order 
of things. I do not indeed deny that to the Production of one thing 
out of another, these forementioned things are requisite, but Genera- 
tion her self is a thing quite distinct from them all. (I finde Aristotle 
in this opinion) and I my self intend to clear it anon, that out of 
the same White of the Egge (which all men confesse to be a similar 
body, and without diversity of parts) all and every the parts of the 
chicken whether they be Bones, Clawes, Feathers, Flesh, or what 
ever else, are procreated and fed. Besides, they that argue thus 
assigning only a material cause, deducing the causes of Natural 
things from an involuntary or casual concurrence of the Elements, 
or from the several disposition or contriving of Atomes ; they doe 
not reach that which is chiefly concerned in the operations of nature, 
and in the Generation and Nutrition of animals, namely the Divine 
Agent, and God of Nature, whose operations are guided with the 
highest Artifice, Providence, and Wisdome, and doe all tend to some 
certaine end, and are all produced, for some certaine good. But these 
men derogate from the Honour of the Divine Architect, who hath 
made the Shell of the Egge with as much skill for the egge's defence 
as any other particle, disposing the whole out of the same matter 
and by one and the same formative faculty." But although these are 
Harvey's theories, it is significant that in his preface he says, "Every 
inquisition is to be derived from its causes, and chiefly from the 
material and efficient", thus expressly excluding formal and final 
considerations. Certainly, as far as his practical work went, he was 
unaffected by them, and in the case of the egg-shell, for example, 
Harvey was not the man to say, "it is present for the protection of 
the embryo", and then to do or say nothing more. Such an explana- 
tion, though he might gladly accept it, was no bar to further explora- 
tion both by way of experiment and observation. 


Harvey not only follows Aristotle in his good discoveries and true 
statements about the egg, but also, unfortunately, in his less useful 
parts, as, for example, when he devotes several pages to the dis- 
cussion of how far the egg itself is alive, and whether there is any soul 
in subventaneous or unfruitful eggs. He decides that there is only 
a vegetative soul. On the other hand, he admirably refutes the 
opinion of those physicians — who were not few in number — who 
declared that the foetal organs were all functionless during foetal life. 
"But while they contende", he says, "that the mother's Blood is 
the nutriment of the foetus in the womb, especially of the Partes 
Sanguineae, the bloody parts (as they call them) and that the Foetus 
is at first, as if it were a part of the mother, sustained by her blood 
and quickened by her spirits, in so much that the heart beats not 
and the liver sanguifies not, nor any part of the Foetus doth execute 
any publick function, but all of them make Holy-Day and lie idle; 
in this Experience itself confutes them. For the chicken in the egge 
enjoyes his own Blood, which is bred of the liquors contained within 
the egge, and his Heart hath its motion from the very beginning, 
and he borroweth nothing, either blood or spirits, from the Hen, 
towards the constitution either of the sanguineous parts or plumes, 
as those that strictly observe it may plainly perceive." We have already 
seen how the Stoics in antiquity believed that the embryo was a part 
of the mother until it was born ; from this idea the transition would 
be easy to the belief that all the organs in the embryo were functionless 
and dependent on the activity of the corresponding ones in the 
maternal organism. 

One of Harvey's most important services to thought lay in his 
abolishing for good the controversy which had gone on ever since 
the sixth century B.C. about which part of the egg was for nutrition 
and which for formation. He had the sense to see that the distinction 
was a useless and baseless one — "There is no distinct part (as we 
have often said) or disposed matter out of which the Foetus may be 
formed and fashioned. . . . An egge is that thing, whose liquors do 
serve both for the Matter and the Nourishment of the foetus.. . .Both 
liquors are the nourishment of the foetus." 

As regards spontaneous generation, Harvey considered that even 
the most imperfect and lowest animals came out of eggs. "We shall 
show", he writes, "that many Animals themselves, especially insects 
do germinate and spring from seeds and principles not to be discerned 


even by the eye, by reason of their contract invisible dimensions (like 
those Atomes, that fly in the aire) which are scattered and dispersed 
up and down by the winds ; all which are esteemed to be Spontaneous 
issues, or born of Putrefaction, because their seed is not anywhere 
seen." Unfortunately, he never returned to this subject, for, as he 
himself informs us in another place, all the papers and notes in his 
house in London were destroyed at the time of the Civil War, so that 
what he had written on the generation of insects irretrievably 

Another point on which Fabricius had been in error was the ap- 
pearance of bone and cartilage in the embryo. According to him, 
"Nature first stretcheth out the Chine Bone, with the ribbes drawn 
round it, as the Keel, and congruous principle, whereon she foundeth 
and finisheth the whole pile". This armchair conceit Harvey was 
easily able to destroy by a mere appeal to experience, but by ex- 
perience also he came upon a fact less easily to be explained, namely, 
that the motion of the foetus began when as yet there was hardly any 
nervous system. "Nor is it less new and unheard of, that there should 
be sense and motion in the foetus, before his brain is made; for the 
Foetus moves, contracts, and extends himself, when there is nothing 
yet appears for a braine, but clear water." On the basis of this 
paradox Harvey may be said to be the discoverer of myogenic con- 
traction, but he already could claim that distinction, for the first 
heart-beats are accomplished long before there are any nerves to the 
heart, as he himself points out. "We may conclude from this fact", 
he remarks, "that the heart and not the brain is the first principle 
of embryonic life", and he gives instances of physiological actions 
not under the conscious control of the individual, such as the reflexes, 
as we should call them, of the intestinal tract, and the emetic action 
of infusion of antimony which cannot be tasted much and "yet there 
passeth a censure upon it by the Stomack" and a vomit ensues. Thus, 
twenty-five years before Francis Glisson, Harvey had formulated, 
from embryological studies, the view that irritability was an intrinsic 
property of living tissues. 

Both Harvey and Fabricius were very puzzled about the first 
origin of the blood. "What artificer", says Harvey, "can transform 
the two liquors into blood, when there is yet no liver in being?" 
It was to be a long time before this question was answered by Wolflf 's 
discovery of the blood islands in the blastoderm, and, even now, the 


chemistry of the appearance of haemoglobin is one of the most obscure 
corners of chemical embryology. The older observers explained it by 
considering the yolk to be akin to blood and ready to turn into it 
at the slightest inducement. 

Another problem which neither Fabricius nor Harvey did any- 
thing to solve was the nature of the air-space at the blunt end of 
the egg. "Fabricius recounts several conveniences arising from it, 
according to its several magnitudes, which I shall declare in short, 
saying, It contains aire in it, and is therefore commodious to the 
Ventilation of the egge, to the Respiration, Transpiration, and Re- 
frigeration, and, lastly, to the Vociferation of the Chicken. Where- 
upon, that cavity is at the first very little, afterwards greater, and 
at last greatest of all, according as the several recited uses do require." 

As regards the placenta, Harvey took the side of Arantius and 
denied any connection between the maternal and foetal circulations. 
"The extremities of the umbilicall vessels", he said, "are no way 
conjoined to the extremities of the Uterine vessels by an Anastomosis, 
nor do extract blood from them, but are terminated in that white 
mucilaginous matter, and are quite obliterated in it, attracting 
nourishment from it." "Wherefore these caruncles may be justly 
stiled the Uterine Cakes or Dugs, that is to say, convenient and 
proportionate organs or instruments designed for the concocting of 
that Albuginous Aliment and for preparing it for the attraction of 
the veins." From this it would appear that Harvey regarded the 
uterine milk as the special secretion of the placenta, conveyed to the 
foetus through the umbilical cord. The nature of the uterine milk 
is still very imperfectly understood (see Section 21). Its discovery is 
usually attributed to Walter Needham, but various remarks in this 
chapter (Ex. lxx) seem to show that Harvey was well acquainted 
with it. In later times, it was regarded by some (Bohnius and 
Charleton in 1686, Zacchias in 1688 and Franc in 1722) as the sole 
source of foetal nourishment. Mercklin spoke of it in 1679 as ''materia 
albuginea, ovique albo non absimili". Harvey often calls the placenta 
the uterine liver, no doubt only for this reason, but the remarkable 
appropriateness of the term was to become apparent in Claude 
Bernard's day. As regards the matter of the continuity of the maternal 
and foetal circulations, he criticises van Spieghel. "There came forth 
a book of late", he says, "wrote by one Adrianus Spigelius, wherein 
he treateth concerning the use of the umbilicall arteries and doth 


demonstrate by powerfull arguments that the Foetus doth not receive 
its Vital Spirits by the arteries from the Mother, and hath fully 
answered those arguments which are alledged to the contrary. But 
he might also as well have proved by the same arguments that the 
blood neither is transported into the Foetus from the mother's veines 
by the propagations of the umbilicall veins which is made chiefly 
manifest by the examples drawn from the Hen-Egge and the Caesarean 

The least satisfactory parts of Harvey's book are the Exercitations 
Lxxi and lxxii on the innate heat and the primigenial moisture. 
Here he becomes very wordy and highly speculative, and gives us 
little but a mass of groundless arguments. He devotes many pages 
to proving that the innate heat is the blood and to drawing distinc- 
tions between blood and gore, the one in the body, the other shed. 
In one place he speaks of the processes of generation as so divine 
and admirable as to be "beyond the comprehension and grasp of 
our thoughts or understanding". Two centuries previously Frasca- 
torius had said precisely the same thing about the motion of the heart, 
and it was ironical that the very man who let the light in on cardiac 
physiology should in his turn despair of the future of our knowledge 
of embryonic development. 

Harvey did not say much about foetal respiration, and his few 
remarks are contained in one of the "additional discourses". He is 
puzzled exceedingly by the question. But he comes very near indeed 
to the truth when he says, "Whosoever doth carefully consider these 
things and look narrowly into the nature of aire, will (I suppose) 
easily grant, that the Aire is allowed to animals, neither for refrigera- 
tion, nor nutrition sake. For it is a tryed thing, that the Foetus is 
sooner suffocated after he hath enjoyed the Aire, than when he was 
quite excluded from it, as if the heat within him, were rather inflamed 
than quenched by the aire". Had Harvey pursued this line of thought, 
and looked still more narrowly into the nature of air, he might have 
anticipated Mayow. He does say that he proposes to treat of the 
subject again, but he never did. 

The mainspring of Harvey's researches on the does and hinds can 
be realised by a reference to Rueff's figures in Fig. 6. According 
to the Aristotelian theory, the uterus after fertile copulation would 
be full of blood and semen ; according to the Epicurean theory (held 
by the "physitians") it would be full of the mixed semina. If this 


coagulated mass exists, said Harvey, it ought to be possible to find 
it by dissection, and this was what he tried to do. It soon became 
plain, as may be read in Ex. lxviii, not only to Harvey but to the 
King and the King's gamekeepers, that no such coagulum existed, 

^t^^^^^jr. S>'^'^^^ ^>^T*-^^J-^ r "^ 
^^^ A--r> >^r'-/f >^'^^ S" ^,-^^ ^ , ■ 

x> f.^^ ^^^^^/s S^^ . rr- f 

Fig. 7. Manuscript notes of Dr William Harvey. 

and the result was made still more certain by means of segregation 
experiments which the King carried out at Hampton Court. Ac- 
cordingly there was nothing to be done but to abandon all the older 
theories completely, and have recourse to some sort of hypothesis 
in which an aura seminalis, an "incorporeal agent" or a "kinde 
of contagious property" should bring about fertilisation. This was 


a perfectly sound deduction from Harvey's experiments, and did not 
then appear anything like so unsatisfactory as it does now, for Gilbert 
of Colchester was not long dead, the "lodestone" was beginning 
to be investigated by the virtuosi, and even such extravagances as 
Sir Gilbert Talbot's Powder "for the sympatheticall cure of wounds" 
were only with difficulty distinguishable from the real effects of 
magnetic force. Harvey's idea of fertilisation by contagion has recently 
been in a sense revived by the work of Shearer (see Section 4*2). 

But to Harvey himself the subject of the action of the seed was 
hid in deep night, and he confessed that, when he came to it, he 
was "at a stand". Some very interesting light is thrown upon his 
mind in this connection by a copy of the De Generatione Animalium 
annotated by himself, and now in the possession of Dr Pybus, by 
whose courtesy and by that of Dr Singer, who has transcribed the 
notes, I have been enabled to study it. It was given by Harvey to 
his brother Eliab, whose name it still bears. The notes, which are 
on the fly-leaves, are written in much the same way as those famous 
ones which Harvey used for his lectures at the College of Physicians in 
London, and which have been reproduced in facsimile. There is the 
same mixture of Latin and English, and the same signs, such as WI, to 
denote thoughts claimed as original. A page is reproduced in Fig. 7. 

For the most part, the notes are uninteresting and nothing but a 
confusion of Aristotelian terms. But one page is concerned with the 
mode of action of the seed, and here we can, as it were, see Harvey's 
mind wrestling with this most difficult of problems. He sees that 
odour and the sense of smell may give a clue. That his thoughts on 
this point were doomed to frustration as soon as eggs and spermatozoa 
were discovered does not detract from the interest of the struggle. 

Quod facit semen fecundum 

What makes the seed fertile is on the analogy of an injection. In fact, 
the injection causes disease in many cases, and that from a distance, both 
by another. . .and by the same. . . A Venereal (?) disease corrupts coitus 
with a woman in whose uterus is the poison. 

They do not [or do not yet ?] come forth in actuality but lie dormant 
as in fuel [? fomite]. Again, rabies in dogs lies dormant for many days 
on my own observation W4. Again, smallpox for days. Again, the genera- 
tive seed, just as it (passes) from the male, lies dormant in the woman as 

Or else like a . . . , like light in stone . . . , the pupil in the eye, in sense 
motion, ... in the body. 


Like ferment, vapour, odour, rottenness ... by rule. 
Or like the smell given off by flowers. 

Like heat, inflammation (?) A in chalk (heat ?) both the wet form 

Like what is first ... in the art of cooking . . . principles of vegetation and 
propagation. A Dormice by hibernating. . .cleansing by water and all 
kinds of lotions, again for insects, as for their seeds as well (?). Or when 
a soul is a god present in nature, that is divine which it brings about 
without an organic body by means of law. 

See Aristode Marvels concerning odours and smells given off. Whether 
on sense and everything that can be smelt gives off something and so 
the objects of disperses (?) what is not without heat, or by destroying . . . 
sense. attracts to itself 

A Amongst inflammable (objects are) fire, naphtha, paper 

A WI manus et odore car . . . anatomia manair. ... 

A Anat . . . post 4°"^ poras. otium inclinente die rursus quod prius et 

olefrere vid. . . . Galen. ... 
A Mr. Boys spainel in Paris lay all ye third night and morning in 
getting dogg. Whelping dogg's sent (scent) are a stronger sent, 
vesting in vestigio alios ord . . . gr . . . lepris odore lepris esse 
libidine esse. Hors, the mare, hors, the cow, a bull per mutta 
A ... si lepra fracedo in farioli fader cupidinitus. Dogg ye otter in aquas 
fracedo vasorum ex sulpore? 

Just as Aristotle put much of his best embryological work into his 
Historia Animalium and not into the work with the appropriate title, 
so Harvey has some admirable observations on the embryonic heart 
scattered through his De Motu Cordis et Sanguinis in Animalibus. Turning 
now to consider Harvey's influence on embryology, we must admit 
that it was in certain respects reactionary. 

1 . He did not break with Aristotelianism, as a few of his pre- 
decessors had already done, but on the contrary lent his authority 
to a moribund outlook which involved the laborious treatment of 
unprofitable questions. 

2. His opposition to atomism and to "chymistry" precluded any 
close co-operation between his followers and those of the Descartes- 
Gassendi tradition. 

3. Fabricius had elaborated a vitalistic theory of differentiation, 
but had allowed growth to be "natural" or mechanical. Harvey, 
however, made both growth and differentiation the results of an 
immanent spirit, a sort of divine legate. 

But these failings are far outweighed by his positive services. It 
must always be remembered that he had no compound microscope. 


and had to rely, like Riolanus, on "perspectives", or simple lenses 
of very low power. 

1. There can be no doubt that the doctrine omne vivum ex ovo 
was a tremendous advance on all preceding thought. Harvey's 
scepticism about spontaneous generation antedated by less than a 
century the experiments of Redi. It is important to note that he was 
led to his idea of the mammalian ovum by observations on small 
conceptions surrounded by their chorion and no bigger than eggs, 
for the true ovum itself was not discovered until the time of de Graaf 
and Stensen. 

2. He identified definitely and finally the cicatricula on the yolk- 
membrane as the spot from which the embryo originated. 

3. He denied the possibility of generation from excrement and 
from mud, saying that even vermiparous animals had eggs. 

4. He discussed the question of metamorphosis (preformation) and 
epigenesis, and decided plainly for the latter, at any rate for the 
sanguineous animals. 

In addition to these achievements, there are others, perhaps less 
striking, but equally important. 

5. He destroyed once and for all the Aristotelian (semen-blood) 
and Epicurean (semen-semen) theories of early embryogeny. This 
was perhaps the biggest crack he made in the Peripatetic teaching 
on development; but, in spite of it, Sennertus, van Linde and 
Sylvius adhered to the ancient views, and Cyprianus, in 1700, 
had the distinction of being the last to support them in a scientific 
discussion, though Sterne, as late as 1 759, referred to them in a way 
that shows they still lived on in popular thought. 

6. He handled the question of growth and differentiation better 
than any before, anticipating the ideas of the present century. 

7. He settled for good the controversy which had lasted for 2200 
years as to which part of the egg was nutritive and which was forma- 
tive, by demonstrating the unreality of the distinction. 

8. He set his predecessors right on a very large number of detailed 
points, such as the nature of the placenta. 

9. He made a great step forward in his theory of foetal respiration, 
though here he did not consolidate the gain. 

10. He affirmed that embryonic organs were active, and that the 
embryo did not depend on external aid for its principal physiological 


But all these titles to remembrance, great as they are, do not 
account for the pecuhar fascination of Harvey. A little of it is perhaps 
due to his imaginative style, which comes out clearly in Martm 
Llewellyn's English version. A word of censure is due to Willis 
for transmuting it in his translation into the dull and pedestrian 
style of 1847. None who reads the 1653 edition of Harvey can ever 
forget such metaphors as this, "For the trunck of the body hitherto 
resembles a skiff without a deck, being in no way covered up by 
the anteriour parts"; or the vigour of diction which promotes such 
remarks as, "In a hen-egge after the tenth day, the heart admits no 
spectators without dissection"; or again, "For while the foetus is yet 
feeble. Nature hath provided it milder diet and solider meats for its 
stronger capacity, and when it is now hearty enough, and can away 
with courser cates, it is served with commons answerable to it. And 
hereupon I conceive that perfect eggs are not onely party-coloured, 
but also furnished with a double white"; or, lastly, "An egge is, as it 
were, an exposed womb ; wherein there is a substance concluded, as 
the Representative and Substitute or Vicar of the breasts". 

In this connection, it would be a pity not to quote from the verses 
which Llewellyn prefixed to his translation of Harvey's book. After 
describing the controversies that followed the De Motu Cordis he wrote 

A Calmer Welcome this choice Peice befall, 

Which from fresh Extract hath deduced all, 

And for Belief, bids it no longer begg 

That Castor once and Pollux were an Egge : 

That both the Hen and Houswife are so matcht, 

That her Son born, is only her Son hatcht; 

That when her Teeming hopes have prosp'rous bin. 

Yet to conceive, is but to lay, within. 

Experiment, and Truth both take thy part: 

If thou canst 'scape the Women ! there's the Art. 

Live Modern Wonder, and be read alone, 

Thy Brain hath Issue, though thy Loins have none. 

Let fraile Succession be the Vulgar Care; 

Great Generation's Selfe is now thy Heire. 

Curiously enough, the "calmer welcome" which Martin Llewellyn 
hoped for actually happened. Harvey's book was so well reasoned 
and based on such good observations that it produced only two 


answers, and they were of little importance. Janus Orcham took 
exception to Harvey's finding no seed in the uterus and suggested 
that it had vaporised like a steam, but his Aristotelian leanings were 
promptly detected and castigated by Rallius. Matthew Slade, taking 
the pseudonym of Theodore Aides, published in 1667 his Dissertatio 
epistolica contra D. G. Harveium, which was, in his own words, "a 
detection of one or two errors in that golden book on the generation 
of animals of William Harvey, greatest of physicians and anatomists". 
The errors were purely anatomical, and ab Angelis defended Harvey 
against Slade's attack, claiming that the "errors" were not errors 
at all. A manuscript work of Slade's appears to be extant. 

Harvey's influence was evidently speedily felt by his contemporaries. 
Strauss soon wrote a rather poor book on the bird's egg in imitation 
of him. But the best instance is that in 1655, very soon after the 
publication of Harvey's book, William Langly, "an eminent senator 
and physician of Dordrecht", made a great many experiments on 
the development of the hen's egg. Buffon says that he worked in 
1635, i.e. before Harvey, but this is not the case, for in his observa- 
tions which were published by Julius Schrader in 1674 the later date 
is given several times. Langly mentions Harvey more than once, 
and evidently followed his example in careful observation, for his 
text is concise and accurate and his drawings very noteworthy. 

Julius Schrader included Langly's work in a composite volume 
containing a well-arranged epitome of Harvey's book on generation 
and some observations of his own on the hen's egg. The book was 
dedicated to Matthew Slade and J. Swammerdam. On the practical 
side Schrader added nothing memorable to Harvey and Langly, but 
it is noteworthy that the mammalian embryo was throughout these 
centuries more popular material than that of the chick. Out of fifty 
embryologists between Harvey and Haller, the names of Langly, 
Schrader, Malpighi and Maitre-Jan practically exhaust the list of 
those who studied the egg of the hen. This rather unfortunate orienta- 
tion of mind doubtless sprang from the strong influence of medicine, 
and especially obstetrics, on seventeenth and eighteenth century 

3-5. Gassendi and Descartes: Atomistic Embryology 

Harvey's death took place in 1657. The following year saw the 
publication of Pierre Gassendi's Opera Omnia, and thus brought in 


an entirely new phase in embryology. Together with Rene Descartes' 
treatise on the formation of the foetus, Gassendi's De generatione 
animalium et de animatione foetus marks a quite different attitude to the 
subject. Harvey had adopted a rather contemptuous position about 
the "corpuscularian or mechanical philosophy", which was then 
coming in, and had expected even less help from it in the solution 
of his problems than from his equally despised "chymists". Gassendi 
now set out to show that the formation of the foetus could be explained 
on an atomistic basis: and, using the Galenic physiology and the 
new anatomy as a framework, he set forth his theory in full. As we 
read it through at the present day, however, we cannot avoid the 
confession that it was not a success. In spite of his frequent 
quotations from Lucretius and his persuasive style, it does not 
carry conviction. The truth of the matter was that the time was 
not ripe for so great a simplification. The facts were insufficiently 
known, and that Gassendi is not quite as interested in them as he is 
in his theory is shown by the circumstance that he only mentions 
Harvey once. 

Gassendi examines in turn the Aristotelian and the Epicurean 
doctrines of embryogeny and rejects them both, the former on the 
ground that the change from tgg to hen is too great and difficult 
for anything so shadowy and ghost-like as a "form" to accomplish, 
and the latter because it leaves no room for teleology. He therefore 
adopts as the basis of his system atomism + preformationism, al- 
leging that all the germs of living things were made at the creation, 
but that they come to their perfection as atomic congregations in an 
atomistic universe. Thomas' monograph is a valuable help to the 
study of this very interesting thinker. 

At exactly the same time, Descartes was speculating on the same 
subject. Added to his posthumous De Homine Liber (1662) is a treatise 
on the formation of the foetus. He may also have written a work 
On the generation of animals, for a manuscript with that title was found 
among his papers after his death, and was believed to be in his 
handwriting. There is evidence, however, that it is not his, and though 
it was published in Cousin's edition of his works, we may safely 
neglect it, agreeing, in the words of that editor, that it is "a fragment 
in which very mediocre and often quite false ideas struggle to light 
through the medium of a style devoid alike of clarity and of grandeur ". 
It must be admitted, however, that even his main treatise is very 


confused. It suffers from containing in its earlier part a great deal 
of matter which really belongs to the physiological text-book which 
immediately preceded it. Thus it begins abruptly in the middle of 
a disquisition on the error of attributing bodily functions to the soul. 
Before long, however, it warms to its theme, and a conception of 
growth is outlined. "When one is young, the movement of the little 
threads which compose the body is less slow than it is in old age, 
because the threads are not so tightly joined one to the other, and 
the streams in which the solid particles run are large, so that the 
threads become attached to more matter at their roots than detaches 
itself from their extremities, so that they grow longer and thicker, 
in this way producing growth." The fourth part of the book is called, 
strangely enough, a Digression, in which the formation of the animal 
is spoken of. The mixture of seeds is then described, and a theory 
of the formation of the heart is attempted by means of an analogy 
with fermentation. The explanation is unconvincing, but has a cer- 
tain interest as showing chemical notions beginning to permeate 
biological thought. However, Descartes' way of looking at develop- 
ment was thoroughly novel, as is illustrated by the following citation. 
"How the heart begins to move.. . .Then, because the little parts 
thus dilated, tend to continue their movement in a straight line, and 
because the heart now formed resists them, they move away from it 
and take their course towards the place where afterwards the base 
of the brain will be formed, they enter into the place of those that 
were there before, which for their part move in a circular manner 
to the heart and there, after waiting for a moment to assemble 
themselves, they dilate and follow the same road as the aforemen- 
tioned ones, etc." Descartes, in fact, with premature simplification, 
was trying to erect an embryology more geometrico demonstrata. 
That he failed in the attempt was as obvious to his contemporaries 
as it is to us — "We see", said Garden, "how wretchedly Descartes 
came off" when he began to apply the laws of motion to the forming 
of an animal". In doing so, he was many years before his time; 
Borelli had done all that could be done at that period in that direc- 
tion, and, significantly enough, he left embryology alone. The rest 
of Descartes' book is exactly like the citations which have been given, 
only applied to each organ and part in turn; he practically uses the 
traditional teaching as a scaffolding in which to interweave his 
mechanical theory, and he discovers no new facts. 


But in the history of embryology these men and their writings have 
a very great significance. Impressed by the unity of the world of 
phenomena, they wished to derive embryology as well as physics 
from fundamental laws. This attempt, which resulted in a Galen- 
Epicurus synthesis on the one hand and a Galen-Descartes synthesis 
on the other, must be regarded as a noble failure. Its authors did not 
realise what a vast array of facts would have to be discovered before 
a mechanical theory could with any justice be applied to explain 
them. Gassendi and Descartes were like the Ionian nature-philo- 
sophers, propounding general laws before the particular instances 
were accurately known. Their ineffectiveness arises from the fact 
that they did not themselves appreciate this, and consequently 
worked out their idea in a prolix detail, the whole of which was 
inevitably doomed to the scrap-heap from the very beginning. But 
the spark was not to die ; and if anywhere in this history we are to 
find the roots of physico-chemical embryology, we must pause to 
recognise them here. 

Much less well known, but not without interest, was the Dissertatio 
de vita foetus in utero of Gregorius Nymmanus, which appeared in the 
same year as the second edition of Descartes' book, 1664. Nymmanus 
writes with a very beautiful Latin style, and expresses himself with 
great clearness. His proposition is, he says, "That the foetus in the 
uterus lives with a life of its own evincing its own vital actions, and 
if the mother dies, it not uncommonly survives for a certain period, 
so that it can sometimes be taken alive from the dead body of its 
mother". In supporting this thesis, Nymmanus answers the argu- 
ments of those who had held that the lungs and heart of the foetus 
were inactive in utero. Fabricius, Riolanus and Spigelius all proved, 
says Nymmanus, that the mother and the foetus by no means neces- 
sarily die at the same time. "The essential life", he says, "is the soul 
itself informing and activating the body, the accidental life is the acts 
of the soul which it performs in and with the body." Though the 
foetus cannot be said to have life in the latter sense, it can in the 
former. The foetus, says Nymmanus, prepares its own vital spirits 
and the instruments of its own soul; there is no nerve between it and 
its mother. If, he says, the foetal arteries got their sphygmic power 
from the maternal heart, they would stop pulsating when the umbilical 
cord was tied, but this is not the case. The pulse of the embryo is 
therefore due to the foetal heart itself. Galen, says Nymmanus, was 


aware of this, but did not understand the meaning of it. Again, the 
foetus in utero moves during the mother's sleep, and vice versa. Nym- 
manus' dissertation is an interesting study in the transition from 
theological to scientific embryology which took place all through the 
seventeenth century, and may be followed in the writings of Varan- 
daeus, de Castro, Dolaeus, Hildanus, Scultetus, Ammanus, Augerius 
and Garmannus. The problem of animation-time, a more meta- 
physical aspect of the same question, was still being handled, but 
less attention was being paid to it than formerly. Honoratus Faber's 
De Generatione Animalium of 1666 does not belong to its period. Its 
author, a Jesuit, proceeds in scholastic fashion to lay down four 
definitions, three axioms, one hypothesis, and seventy-seven pro- 
positions, in the last of which he summarises his conclusions. He is 
interesting in that he displayed a disbelief in spontaneous generation, 
thereby anticipating Redi, and he is careful to mention the work of 
Harvey, but nevertheless his treatise is of little value. His chief 
importance is that he is an epigenesist, and therefore demonstrates 
to us how the true opinion was becoming accepted, when Malpighi's 
brilliant observations and bad theory sent it out of favour, and pre- 
pared the way for the numerous controversies of the following 

3-6. Walter Needham and Robert Boyle 

It was in 1666 also that the following appeared in the Philosophical 
Transactions of the Royal Society : 

A way of preserving birds taken out of the egge, and other small f actus' s: 
communicated by Mr. Boyle. 

When I was sollicitous to observe the Processe of Nature in the Forma- 
tion of the Chick, I did open Hens Eggs, some at such a day, and some 
at other daies after the beginning of the Incubation, and carefully taking 
out the Embryo's, embalmed each of them in a distinct Glass (which is 
to be carefully stopt) in Spirit of Wine; Which I did, that so I might have 
them in readinesse to make on them, at any time, the Observations, I 
thought them capable of affording; and to let my Friends at other seasons 
of the year, see, both the differing appearances of the chick at the third, 
fourth, seventh, fourteenth, or other daies, after the eggs had been sate 
on, and (especially) some particulars not obvious in chickens, that go 
about, as the hanging of the Gutts out of the Abdomen, etc. How long 


the tender Embryo of the Chick soon after the Punctum saliens is 
discoverable, and whilst the bodie seems but a little organized Gelly, 
and some while after that, will be this way preserv'd, without being 
too much shrivel'd up, I was hindred by some mischances to satisfie 
myself; but when the Faetus's, I took out, were so perfectly formed 
as they were wont to be about the seventh day, and after, they so 
well retained thjeir shape and bulk, as to make me not repent of my 
curiosity; And some of those, which I did very early this Spring, I can 
yet shew you. 

Boyle said in conclusion that he sometimes also "added Sal 
Armoniack, abounding in a salt not sowre but urinous". 

In the same year that Nymmanus' book appeared, Nicholas 
Stensen, that great anatomist, later a Bishop, who was also to all 
intents and purposes the founder of geology, published his De musculis 
et glandulis specimen, in which Goiter's observations on the vitelline 
duct and the general relations between embryo and yolk in the hen's 
tgg were made again and confirmed. About this time also Deusingius 
described his case of abdominal pregnancy, and was thus the first 
anatomist to draw attention to this phenomenon. 

In 1667 Stensen published his Elementorum myologiae specimen, in 
which he described the female genital organs of dogfishes. He 
demonstrated eggs in them and affirmed that the "testis" of women 
ought to be regarded as exactly the same organ as the "ovary" or 
"roe" of ovipara. At the time he carried the suggestion no further, 
but it was an extremely fruitful one, and it is surprising that it did 
not create more interest, for it was exactly what Harvey had been 
looking for. Nothing obvious having been found in the uteri of King 
Charles' does, and the conviction yet being very strong that viviparous 
conceptions really came from eggs, Stensen's minute ova supplied 
the fitting answer to the question. Thus Harvey and Stensen between 
them substituted the modern knowledge of mammalian ova for the 
ancient theory of the coagulum all in the space of fourteen years. The 
other event for which the year 1667 is remarkable is the De Formato 
Foetu of Walter Needham. Needham was a Cambridge physician 
who went to Oxford to study in the active school of physiological 
research which such men as Christopher Wren, Richard Lower, John 
Ward and Thomas Willis were making famous. His book on the 
formation of the embryo, written later (and dedicated to Robert 
Boyle), after he had been in practice in Shropshire for some time. 


is important because it is the first book in which definite chemical 
experiments on the developing embryo are reported, and also 
because it contains the first practical instructions for dissections of 

Sir Thomas Browne had, as we have already seen, made experi- 
ments of a chemical nature on the constituents of birds' eggs and of 
the eggs of amphibia, but he did not analyse them after any develop- 
ment had been allowed to take place. He may therefore be regarded 
as the father of the static aspect of physico-chemical embryology, 
while Walter Needham may be regarded as the founder of the 
dynamic aspect. The practical difficulties of these pioneers of animal 
chemistry may be seen in such a book of practical instructions as 
Salmon's General Practise ofChymistry of 1678. They had no satisfactory 
glassware, no pure reagents, the methods of heating were incredibly 
clumsy, and there was no means of measuring either heat or atmo- 
spheric pressure. 

In the review of Needham's book which is to be found in the 
Philosophical Transactions of the Royal Society for September 1667 there 
occurs the sentence, "These humors (the amniotic, allantoic, etc.) 
he saith, he hath examined, by concreting, distilling, and coagulating 
them; where he furnishes the Reader with no vulgar observations". 
What were these observations ? They are to be found in the chapter 
entitled "The nature of the humours": 

"I now proceed to speak of this other nutritive liquor round about 
the urine itself which latter is plainly separated by the kidneys and 
the bladder. These liquors also proceed from the blood and seem 
similar to its serum but yet they are different from it. For when fire 
is applied to them in an evaporating basin [cochlea] they do not 
coagulate, as the blood-serum always does. Indeed, not even the 
colliquamentous liquid of the egg itself coagulates in this manner, 
although it is formed from juices which are evidently liable to coagu- 
lation — in the same way humours differ from themselves before and 
after digestion, filtration, and the other operations [mangonial of 
nature. All, when distilled, give over a soft and clear water [mollem 
et lenem] very like distilled milk. This property is common to the liquor 
of the allantoic space, along with the rest. Because when the salts 
are not yet made wild and exalted the serum of the blood remains 
still quite soft and does not give proof of a tartaric or saline nature. 
Indeed, the first urine of an infant is observed by nurses to be not at 


all salt, but in older animals, when I distilled it in an alembic, I 
seemed to observe a little volatile salt at the small end [in capitello]. 
Coagulations attempted by acids happened differently in respect of 
the different humours. For when I poured a decoction of alumina 
into the liquor of the cow's amnios it exhibited a few rather fine 
coagulations but they were clearly white. The allantoic juice, how- 
ever, was precipitated like urine. Spirits of vitriol and vinegar 
brought about less results than alumina in each case. Spontaneous 
concretions I found also in the later months; these I discovered in 
both places. They are more frequent and larger, however, within 
the allantoic membrane." 

From the above excerpt, which contains the account of all that 
Needham did on the chemical composition of the embryonic liquids, 
it can be seen that he treated the whole matter more dynamically 
than Browne. He was the first to describe the solid bodies in the 
amniotic fluid (see Jenkinson) and his chemical experimentation was 
all pioneer work. 

His book has other merits, however. In the first chapter, he refutes 
the theory which Everard had propounded, that the uterine milk was 
identical with the contents of the thoracic duct, conveyed by lym- 
phatic vessels to the uterus from the lac teals of Aselli, instead of 
elsewhere, and he shows that arteries must be the vessels bringing 
the material to the womb. The second chapter deals with the placenta 
"where he giveth a particular account of the double Placenta or 
Cake, to be found in Rabbets, Hares, Mice, Moles, etc., and examines 
the learned Dr Wharton's doctrine, assigning a double placenta to at 
least all the viviparous animals, so as one half of it belongs to the 
Uterus, the other to the Chorion, shewing how far this is true, and 
declaring the variety of these Phaenomena. Where do occur many 
uncommon observations concerning the difference of Milk [uterine] 
in ruminating and other animals, the various degrees of thickness of 
the uterin liquor in oviparous and viviparous creatures". He de- 
scribes the human placenta very correctly indeed. "The use of the 
placenta is known to be to serve for conveighing the aliment to the 
foetus. The difficulty is only about the manner. Here are examined 
three opinions, of Curvey, Everhard, and Harvey. The two former 
do hold that the foetus is nourished only from the Amnion by the 
mouth ; yet with this difference, that Curvey will have it fed by the 
mouth when it is perfect, but whilst it is yet imperfect, by filtration 


through all the pores of the body, and by a kind of juxtaposition : but 
Everhard, supposing a simultaneous formation of all the instruments 
of nutrition together and at first, and esteeming the mass of bloud 
by reason of its asperity and eagerness unfit for nutrition, and rather 
apt to prey upon than feed the parts, maintains, that the liquor is 
sucked out of the amnion by the mouth, concocted in the stomack, 
and thence passed into the Milky Vessels even from the beginning. 
Meantime they both agree in this, that the embryo doth breath but 
not feed through the umbilicall vessels. This our Author undertakes 
to disprove; and having asserted the mildness of, at least, many 
parts of the bloud, and consequently their fitness for nutrition, he 
defends the Harveyan doctrine of the colliquation of the nourishing 
juyce by the Arteries and its conveyance to the foetus by the 

In the third chapter Needham gives the first really comparative 
account of the secondary apparatus of generation, enunciating the 
rather obvious rule that in any given case the number of membranes 
exceeds the number of separate humours by one. He affirms that 
all the humours are nutritive save the allantoic. It had previously 
been held that all fish eggs were of one humour only, but he points 
out that a selachian egg has its white and yolk separate. He gives 
the results of his chemical experiments at this point, and suggests 
that the noises heard from embryos in utero and in ovo may be due 
to the presence of air or gas in the amniotic cavity, thus forming a 
link between Leonardo and Mazin. In his fourth chapter he deals 
with the umbilical vessels and the urachus, and here he claims priority 
over Stensen for the discovery of the ductus intestinalis in the chick, 
referring to Robert Boyle, Robert Willis, Richard Lower and Thomas 
Millington, to whom, he says, he showed the duct before Stensen 
published his observations on it. The fifth chapter is concerned with 
the foramen ovale, and the arterial and venous canals, and with the 
foetal circulation in general. The sixth is about respiration or "bio- 
lychnium", and in it Needham writes against the conception of a 
vital flame, alleging cold-blooded animals, etc., in his favour, but 
here he takes a retrograde step, for he argues that the use of the lungs 
is not for respiration but to "comminute the bloud and so render 
it fit for a due circulation". "The seventh and last chapter contains 
a direction for the younger Anatomists, of what is to be observed in 
the dissection of divers animals with young, and first, of what is 


common to the viviparous, then, what is pecuHar to severall of them, 
as, a sow, mare, cow, ewe, she-goat, doe, rabbet, bitch, and a woman, 
lastly, what is observable in an Egg, skate, salmon, frog, etc. All is 
illustrated with divers accurate schemes." 

The subsequent course of chemical embryology in the seventeenth 
century may be put in a very few words. Marguerite du Tertre 
incorporated in her obstetrical text-book of 1677 the results of some 
similar experiments to those of Needham. "If you heat the (amniotic) 
liquor", she says, "it does not coagulate, and if you boil it it flies 
away leaving a crass salt like urine, but if you heat the serosity of 
blood, it solidifies as if it were glue." The same observation was re- 
corded by Mauriceau in 1687, who concluded, with some common 
sense, that, as there was so little solid matter present, the liquid could 
not be very nutritive; and by Case in 1696, who said, "In this juice 
the plastic and vivifying force resides, for although to our eyes it looks 
in colour and consistency like the serum of the blood, yet it is abso- 
lutely \toto coelo] different; for if a little of the former is slowly evaporated 
\si in cochleari super ignem defines] no coagulation will ever appear." 
Lister said this once more in 171 1, but with Boerhaave's work of 1732 
the subject entered a new phase. 

In 1670 Theodore Kerckring published an adequate work on foetal 
osteology, and, two years later, de Graaf and Swammerdam, 
making full use of the opportunities afforded them by the invention 
of the microscope, described in detail the ova of mammalia, thus 
demonstrating the truth of Stensen's suggestion of some years before. 
It is important to note that these workers mistook the "Graafian 
follicles" for the eggs — a mistake which was not rectified till the time 
of von Baer. Stensen himself published not long after an account 
of these eggs also, but he was by then too late to gain the priority 
of demonstration. Portal's claim that Ferrari da Grado, who lived 
in the fifteenth century, was the true discoverer of mammalian ova 
has been disproved by Ferrari; and, although it is true that Volcher 
Goiter described what we now call the Graafian follicles, he did not 
recognise in any way their true nature. 

De Graaf 's discovery was confirmed in 1678 by Caspar Bartholinus, 
and, in 1674, by Langly, whose original observations had been made, 
so it was said, in 1657, the year of Harvey's death. If this is true, 
Langly has the priority of observation, Stensen of theory and de 
Graaf of demonstration. 


3-7. Marcello Malpighi: Micro- Iconography and Preforma- 

In the year 1672, Marcello Malpighi, who had for many years 
previously been working on various embryological problems with the 
aid of the simple microscope, published his tractates De Ovo Incubato 
and De Formatione Pulli in Ovo. In spite of its great importance, there 
is not much to be said about it, for it is anything but a voluminous 
work. The plates in which Malpighi represented the appearances he 
had seen in his examination of the embryo at different stages are 
beautiful, and some of them are reproduced. Description of the embryo 
was now pushed back into the very first hours of incubation, and it 
is interesting to note that Malpighi could not have done his work 
without Harvey, whose name he mentions on his first page, and who 
pointed out the cicatricula as the place where development began, 
and therefore, as Malpighi must have reasoned, the place where 
microscopic study would be very profitable. Now for the first time 
the neural groove was described, the optic vesicles, the somites, and 
the earliest blood-vessels. 

Malpighi opened the modern phase of the controversy preformation 
versus epigenesis by supporting the former view. Embryogeny, he 
held, is not comparable to the building of an artificial machine, in 
which one part is made after another part, and all the parts gradually 
"assembled", but takes place rather by an unfolding of what was 
already there, like a Japanese paper flower in water. He was led 
to this belief by the fact that development goes on after fertilisation 
as the tgg passes down the oviduct, and in the most recently laid 
eggs gastrulation is already over, so that in his researches he could 
never find an absolutely undivided egg-cell. It is curious to note 
that he says his experiments were done "mense Augusti, magno vigente 
calore'\ so that more than a usual degree of development would 
have taken place overnight. Had he examined the cicatriculae in 
hens' eggs before laying, he would very probably not have formed 
this theory, and the epigenesis controversy would have been settled 
with Harvey. Another influence which was unfavourable to the 
epigenetic position was that it was Aristotelian, and therefore un- 
fashionable. Yet Malpighi's view was much more sensible than many 
which succeeded it, for he did not maintain a perfectly equal swelling 
up of all parts existing at the start, but rather an unequal unfolding, 

SECT. 3] 



a distribution of rate of growth at different times and in different 
regions of the body. Thus he says, "Now, as Tully says, Death truly 
belongs neither to the living nor to the dead, and I think that some- 
thing similar holds of the first beginnings of animals, for when we 
enquire carefully into the production of animals out of their eggs, 
we always find the animal there, so that our labour is repaid and we 
see an emerging manifestation of parts successively, but never the 
first origin of any of them". 

Ti£ JCr 

I>e Cue . 


#1? J 


Ti^ lOI. 

Fig. 8. Malpighi's drawings of the early stages of development in the chick embryo. 

What had been an unfounded speculation for Seneca in antiquity 
and for Joseph de Aromatari and Everard in late times was now set 
upon an apparently firm experimental basis by Malpighi. 

It is most instructive to note the difference in the attitudes of 
Langly and Schrader respectively towards the preformation question. 
Langly has no doubts about it, nor has Faber; they both follow 
Harvey and epigenesis unquestioningly, but Schrader, although he 
believes in epigenesis on the whole, is not at all certain about it. 
His friend, Matthew Slade, he says, brought the epistle of Joseph 
de Aromatari to his attention, and what with that and the unexplained 
observations of Malpighi on the pre-existence of the embryo, he is 
not willing to deny all value to preformationist doctrine. Others 
were bolder. It was immediately seized upon by Malebranche, the 

1 68 


Streeter of his age, who, in his Recherche de la Verite of 1672, reaHsed 
its philosophical possibilities, and gave it a kind of metaphysical 
sanction. That mystical microscopist, Swammerdam, made use of 
it as an explanation of the doctrine of original sin. In a remarkably 
short space of time it was a thoroughly established piece of biological 

Malebranche refers to it in his Recherche de la Verite in the chapter 
where he treats of optical illusions and emphasises the deceitfulness 
and inadequacy of our senses. "We see", he says, "in the germ of a 
fresh Qgg which has not been incubated an entirely formed chicken. 
We see frogs in frogs' eggs and we shall see other animals in their 


Fig. 9. Malpighi's drawings of the chick embryo's blood-vessels. 

germs also when we have sufficient skill and experience to discover 
them. We must suppose that all the bodies of men and animals which 
will be born until the consummation of time will have been direct 
products of the original creation, in other words, that the first females 
were created with all the subsequent individuals of their own species 
within them. We might push this thought further and belike with 
much reason and truth, but we not unreasonably fear a too premature 
penetration into the works of God. Our thoughts are, indeed, too 
gross and feeble to understand even the smallest of his creatures." 
Malebranche, who was a priest of the Oratory of the Cardinal de 
Berulle, took an ardent interest in the scientific life of his time — for 
example, in a letter to Poisson, the Abbe Daniel wrote, "Reverend 
Father, M. Malebranche has written to me saying that he has in- 
stalled an oven in which he has hatched eggs. He has already opened 



lu Ouc 


Showing the early stages of the development of the chick, somites, area vasculosa, etc. 


some and has been able to see the heart formed in them and beating, 
together with some of the arteries" (Blampignon). 

Swammerdam's support for preformation came from a different 
angle. He had been investigating insect metamorphosis, and, having 
hardened the chrysalis with alcohol, had seen the butterfly folded 
up and perfectly formed within the cocoon. He concluded that the 
butterfly had been hidden or masked {larvatus) in the caterpillar, and 
thence it was no great step to regard the Qgg in a similar light. Each 
butterfly in each cocoon must contain eggs within it which in their 
turn must contain butterflies which in their turn must contain eggs, 
and so on. Before long, Swammerdam extended this theory to man. 
"In nature", he said, "there is no generation but only propagation, 
the growth of parts. Thus original sin is explained, for all men were 
contained in the organs of Adam and of Eve. When their stock of 
eggs is finished, the human race will cease to be." 

In 1684 Zypaeus reported that he had seen minute embryos in 
unfertilised eggs, and there were other similar claims. ''^Hinc recentiores 
physiologV\ said Schurigius in 1732, ^^ hominem in ovulis delineatum 
quoad omnes partes in exiguis staminibus ante conceptionem existere 

Swammerdam cannot be regarded simply as one of the principal 
pillars of the preformation theory. His own embryological researches, 
which were made chiefly on the frog, were remarkable in many 
ways. He was the first to see and describe the cleavage of the egg- 
cell and later segmentation. He said that there was a time during the 
development of the tadpole when its body consisted of granules 
{greynkens or klootkens), but as these grew smaller and much more 
numerous they escaped his penetration. Leeuwenhoek also saw these 
cells, and his account was published long before Swammerdam's, 
but his observations on the rotating embryos oi Anodon and the eggs 
of fleas were equally interesting. 

3-8. Robert Boyle and John Mayow 

In 1674 John Mayow, a young Oxford physician, published his 
tractate, De Respiratione Foetus in Utero et Ovo, which was included as 
one of the parts of his Tractatus Quinque medico-physici in that year. 
Mayow was the first worker to realise that gaseous oxygen, or, as he 
termed it, the " nitro-aerial " vapour, was the essential factor in the 
burning of a candle and the respiration of a living animal. His work 


was forgotten until Beddoes drew attention to it in 1 790, but since then 
many have praised it and Schultze makes him the equal of Harvey. 

The reason why he became interested in embryology is given in 
the opening sentences of his work. "Since the necessity of breathing", 
he says, "is so essential to the sustaining of life that to be deprived 
of air is the same as to be deprived of common light and vital spirit, 
it will not be out of place to enquire here how it happens that the 
foetus can live though imprisoned in the straits of the womb and 
completely destitute of air." He first of all gives an account of the 
opinions held about foetal respiration and the umbilical cord. He 
says that he disagrees (i) with the view that the embryo breathes 
per OS while it is in the womb, for there is no air in the amnion and 
the suctio infantuli proves nothing; and (2) with the view pro- 
pounded by Spigelius that the umbilical vessels existed to supply 
blood to the placenta for the nourishment of the latter. If this were 
the case, he says, the membranes in the hen's egg could not be formed 
before the vitelline vein, as they are, and in cases of foetal atrophy 
the placenta would always die and be corrupted too, which does not 
happen. Nor does he support the view of Harvey (3) that the 
umbilical vessels supply blood for the concoction and colliquation 
of the food of the foetus, for why should not the embryonic body 
prepare its own nutritious juice before birth just as it does afterwards. 
He further thinks the theory (4) that the umbilical vessels are for 
carrying off surplus foetal nourishment quite untenable and as little 
likely as the theory (5) that they exist for the object of allowing a 
foetal circulation — for this could just as well be accomplished through 
the vessels which exist in the embryonic body. 

Mayow decides therefore for the opinion of divino sene Hippo- 
crate and Everard that the umbilicus is a respiratory mechanism, 
carefully dissociating himself, however, from the hypothesis of 
Riolanus that the umbilical cord with all its windings is so arranged 
to cool the blood passing through it. He then says, "We observe, 
in the first place, that it is probable that the albuminous juice exuding 
from the impregnated uterus is stored with no small abundance of 
aerial substance, as may be observed from its white colour and frothy 
character [Needham's uterine milk]. And in further indication of 
this, the primogenial juices of the egg, which have a great resemblance 
to the seminal juice of the uterus, appear to abound in air particles. 
For if the white or the yolk of an tgg be put into a glass from which 


the air is exhausted by the Boyhan pump these liquids will imme- 
diately become very frothy and swell up into an almost infinite 
number of little bubbles and into a much greater bulk than before — a 
sufficiently clear proof that certain aerial particles are most intimately 
mixed with these liquids. To which I add that the humours of an 
tgg when thrown into the fire, give out a succession of explosive 
cracks which seem to be caused by the air particles rarefying and 
violently bursting through the barriers which confined them. Hence 
it is that the fluids of the egg are possessed of so fermentative a nature. 
For it is indeed probable that the spermatic portions of the uterus 
and its carunculae are naturally adapted for separating aerial particles 
from arterial blood. These observations premised, we maintain that 
the blood of the embryo, conveyed by the umbilical arteries to the 
placenta or uterine carunculae, brings not only nutritious juice, but 
along with this a portion of nitro-aerial particles to the foetus for 
its support, so that it seems that the blood of the infant is impregnated 
with nitro-aerial particles by its circulation through the umbilical 
vessels quite in the same way as in the pulmonary vessels. And there- 
fore I think that the placenta should no longer be called a uterine 
liver but rather a uterine lung". These splendid words, informed by 
so much insight and scientific acumen, show that, by the time of 
Mayow, chemical embryology had definitely come into being. He died 
at the early age of thirty-six, and we may well ponder how different 
the subsequent course of this kind of study would have been if he had 
lived a little longer. 

The second part of Mayow's treatise is concerned with respiration 
in the hen's egg during its development, and it may be noted that 
his observations on the air contained in the liquids before develop- 
ment probably account for the facts which have been reported at 
one time and another concerning an alleged anaerobic life of embryos 
in early stages. Mayow is wrong in supposing that the gas which he 
pumped out from white and yolk was purely "nitro-aerial", but he 
shows the greatest good sense in his reminder that the amount of 
nitro-aerial particles required by embryos must be comparatively 
small owing to their small requirement for "muscular contraction 
and visceral concoction". His remarks on the effect of heat on the 
developing egg are not so clear as the remainder of the treatise, but 
he seems to mean that the heat will disengage the nitro-aerial particles 
from the liquids, and so aid in respiration, an idea which was later 


used by Mazin. His fundamental mistake here was that he failed to 
realise that the egg-shell was permeable to air; and this vitiates all 
his reasoning about the respiration of the egg. "It will not be ir- 
relevant", he says, "to enquire here whether the air which is con- 
tained in the cavity in the blunter end of every egg contributes to 
the respiration of the chick." He first notes that the cavity in question 
lies between two membranes and not between the shell-membrane 
and the shell as Harvey himself had supposed ; and then he goes on 
to say that he disagrees with the opinion of Fabricius, who had asserted 
that the air in the air-space serves for the respiration of the chick. 
His reasons are (i) that there would not be enough therein for the 
needs of the embryo which would use it, as it were, in one gulp, 
and (2) that the air in it cannot pass through the inner membrane, 
an error into which he was led by observing that, if an egg-shell 
with its contents removed and its air-space intact, was put into a 
vacuum, the air-space would swell up until it was as big as the egg 
itself. Mayow sees now what had escaped the attention of all previous 
observers, namely, that the egg-contents are not "rarefied or ex- 
panded, but are on the contrary condensed and forced into a nar- 
rower space than before". Such a condensation could, he thinks, 
take place in four ways, (a) by an increase in propinquity of discrete 
particles, (b) by a subsidence of motion on the part of a congregation 
of particles into rest, (c) by the extraction of some subtle spirit from 
amongst the particles, and, (d) by a decrease in elasticity on the part 
of some elastic substance previously present. We should at the present 
time choose the third alternative as being the truest, in view of the 
loss of water and carbon dioxide which the egg suffers as it develops, 
but Mayow chose the fourth, thinking it probable that the "air 
distributed among the juices of the egg loses its elastic force on account 
of the fermentation produced among these juices by incubation". 
Now since the egg-contents are compacted into smaller bulk by the 
process of incubation, a vacuum would be created somewhere if 
Nature had not, with her customary prudence, inserted a small 
amount of air into the air-space which might in due course expand 
and avoid this. His proof for this was an inaccurate observation; 
he thought he saw, in eggs at a late stage, when the contents were 
removed, the air-space collapse to the normal size which it occupies 
in unincubated eggs. He expressly says that his theory does not depend 
upon the conception of horror vacui, but that, by the compressive 


action of the imprisoned air, the fluids of the egg would be forced into 
the umbiHcal vessels, and the particles composing the embryonic body 
packed more tightly together. "The internal air appears to perform 
the same work as the steel plate bent round into numerous coils by 
which automata are set in motion." 

With this ingenious but erroneous supposition Mayow concludes 
what is undoubtedly the first great contribution to physiological or 
biophysical embryology. His views on foetal respiration were soon 
generally accepted, as the writings of Zacchias, Viardel, Pechlin and 
John Ray show, but Sponius as late as 1684 was asserting that the 
lungs of the foetus were functional in utero, absorbing from the 
amniotic liquid the nitro-aerial particles which P. Stalpartius sup- 
posed the placenta to be secreting into it. It is interesting to note 
that by Mayow's own air-pump method Bohn found nitro-aerial 
particles in the uterine milk in 1686, and Lang found them in the 
amniotic liquid in 1 704. The problem had by then arrived at a stage 
beyond which it could not progress in the absence of quantitative 

The year 1675 saw the publication of Nicholas Hoboken's useful 
treatise on the anatomy of the placenta, and of the English edition 
of P. Thibaut's Art of Chymistry. I mention the latter here, because 
of a reference to the special conditions of embryonic life which is 
found in it. As yet no real help was being given to embryology by 
contemporary chemistry. 

The Magistery and Calx of Egg-shells. 

Obs. 2. That you must use the eggshells of hens and not of ducks, geese, 
or turkeys because that hens eggshells easier calcin'd being thinner by 
reason that a hen is a more temperate animall; waterfowl are hotter and 
by reason of their heat do concoct and harden their eggshells more than 
other fowl ; and from thence it comes that you must have a greater quantity 
of your Dissolvant, employ more heat, and spend more time to calcine 
the eggs of waterfowl than those of hens. 

About this time also Francis Willoughby published his famous 
book on birds, an attempt to bring Aldrovandus up to date, in which 
a good picture is given of the embryological knowledge of the time, 
although no new observations or theories are given. Another con- 
temporary review is that of Barbatus. 

In 1677, spermatozoa were discovered, as announced by Hamm 
and Leeuwenhoek in the Philosophical Transactions of the Royal Society, 


though Hartsoeker afterwards claimed that he had seen them as 
early as 1674, but had not had sufficient confidence to publish his 
results. There is a reference to this in the letters of Sir Thomas 
Browne, who, writing to his son, Dr Edward Browne, on December 9, 
1679, said, "I sawe the last transactions, or philosophicall col- 
lections, of the Royal Society. Here are some things remarkable, as 
Lewenhoecks finding such a vast number of little animals in the melt 
of a cod, or the liquor which runnes from it ; as also in a pike ; and 
computeth that they much exceed the number of men upon the whole 
earth at one time, though hee computes that there may bee thirteen 
thousand millions of men upon the whole earth, which is very many. 
It may bee worth your reading". 

At the same time as these events were taking place, Robert Boyle, 
at Oxford and London, was engaged in carrying out those experi- 
ments in chemistry which led him before long to write his Sceptical 
Chymist. It is not generally known that in this work, which appeared 
in 1680, and which set the key for the whole spirit of subsequent 
physico-chemical research, Boyle has a reference to embryology, and, 
curiously enough, in connection with a point which, although it is 
easily seen to be of the highest importance, has been quite overlooked 
by the commentators upon him. One of the main things he was 
trying to urge was that, until some system could be proposed which 
would give a means of quantitative estimation of the constituents of 
a mixture, no further progress would be made. He was asking, in 
fact, that chemistry should become an exact science, and his demand 
is only veiled by the unfamiliarity of his language. His preference 
for the "mechanical or corpuscularian" philosophy was mainly due 
to his realisation that, unless chemistry was going to start measuring 
something, it might as well languish in the obscurity to which 
Harvey would have willingly relegated it. Thus he says, "But I 
should perchance forgive the Hypothesis I have been all this time 
examining (that of the alchemists), if, though it reaches but to a 
very little part of the world, it did at least give us a satisfactory account 
of those things which 'tis said to teach. But I find not that it gives 
us any other than a very imperfect information even about mixt 
bodies themselves; for how will the knowledge of the Tria Prima 
discover to us the reason why the Loadstone drawes a Needle, and 
disposes it to respect the Poles, and yet seldom precisely points at 
them? how will this hypothesis teach us how a Chick is formed 

SECT. 3] 



in the Egge, or how the seminal principles of mint, pompions, and 
other vegetables, can fashion Water into various plants, each of them 
endow'd with its peculiar and determinate shape and with divers 
specifick and discriminating Qualities? How does this hypothesis 
shew us, how much Salt, how much Sulphur, how much Mercury must be 
taken to make a Chick or a Pompion? and if we know that, what 
principle is it, that manages these ingredients and contrives, for 
instance, such liquors as the White and Yolke of an Egge into such 
a variety of textures as is requisite to fashion the Bones, Arteries, 
Veines, Nerves, Tendons, Feathers, Blood and other parts of a Chick; 
and not only to fashion each Limbe, but to connect them altogether, 
after that manner which is most congruous to the perfection of the 
Animal which is to consist of them? For to say that some more fine 
and subtile part of either or all the Hypostatical Principles is the 
Director in all the business and the Architect of all this elaborate 
structure, is to give one occasion to demand again, what proportion 
and way of mixture of the Tria Prima afforded this Architectonick 
Spirit, and what Agent made so skilful and happy a mixture?" 
Boyle's instance of the magnetic needle pointing nearly, not exactly, 
at the north, and his use of the expressions "how much, how many, 
proportion, way of mixture", indicate that he was moving towards 
a quantitative chemistry, and by express implication a quantitative 
embryology. Elsewhere he says that he thinks the Tria Prima will 
hardly explain a tenth part of the phenomena which the "Leucip- 
pian" or atomistic hypothesis is competent to deal with. Thus, 
although Boyle made few experiments or observations on embryos, 
he occupies a very important position in the history of embryology. 
During the last two decades of this century, the Oxford Philo- 
sophical Society were occupied on a good many occasions with 
problems relating to embryology. It is extremely interesting to note, 
in connection with what we have just seen in Boyle, that John 
Standard of Merton College reported on February 10, 1685, "the 
following obbs. concerning ye weight of ye severall parts of Henn's 
eggs ; done with a pair of scales which turned with \ a grain. 

ozs. dr. 

A henn's egg weighed 2 

The skin weighed 

The shell 
The yolk 
The white 





Loss in weighing 



ozs. dr. scr. grns. 

Another raw egg of the same sort ... 2 i 2 13 


The former egg boiled 

Lost in boiling 

The skin 

The shell 

The yolk 

The white 

2 I I 19 

.2 I I 18 

• - - - 15 


- I 2 19 

- 5 - 7 
I 2 - 13 

Loss in weighing 5 

Another early quantitative observation was that of Claude Perrault 
who found about 1680 that developing ostrich eggs lost one-ninth 
of their weight in five weeks. The Oxford Philosophical Society, 
however, preferred as a rule to consider more unusual things, such 
as "the egges of a parrot hatched in a woeman's bosome, a hen egg 
figur'd like a bottle, a hen egg that at the big ende had a fleshie 
excrescence, another hen-eg, monstrous, a suppos'd cocks egg, and 
the eggs of a puffin, an elligug, and a razor-bill". Mention of these 
different kinds of eggs reminds us that the systematic collection and 
classification of eggs had been begun some years before by Sir Thomas 
Browne (as may be seen in John Evelyn) and by John Tradescant. 
About this time R. Waller made some noteworthy observations on 
the "spawn of frogs and the production of Todpoles therefrom", 
extending the work begun by Swammerdam not long before. 
Mauriceau now gave a description of the phenomenon of sterile 
foetal atrophy. The century fittingly closes with Michael Ettmiiller's 
ponderous treatise, in which all the embryological work of the 
seventeenth century is summarised with considerable accuracy. He 
supported the moribund menstruation theory of embryogeny with 
the argument that animals do not menstruate because they are more 
prolific than men, and therefore all their blood is required for genera- 
tion. Garmann's Oologia curiosa, which appeared in 1691, is worth 
mention also, as a review of the knowledge of the time. But that his 
work was what the booksellers' catalogues describe as "curious" is 
shown by the following chapter-headings: De ovo mystico, rnpthico, 
magico, mechanico, medico, spagyrico, magyrico, pharmaceutico. 

3-9. The Theories of Foetal Nutrition 

During the course of the seventeenth, and the first quarter of the 
eighteenth, century, many theories were propounded concerning 
foetal nutrition. It is convenient to classify them. 


I. That the embryo was nourished by the menstrual blood. 

Beckher, 1633. 

Plempius, 1644. (He did not deny that the umbilical cord was 

functional, but insisted that the blood passing through it was 


In 1 65 1 Harvey's work was published. 
Sennertus, 1654. 
Seger, 1660. 
van Linde, 1672. 
F. Sylvius, 1680. 
Cyprianus, 1700. 

II. That the embryo was nourished by its mouth. 
{a) By the amniotic liquid. 

(A) In addition to the umbilical blood. 
Harvey, 1651. 
W. Needham, 1667. 
de Graaf, 1677. 

C. Bartholinus, 1679. 
van Diemerbroeck, 1685. 
Ortlob, 1697. 

D. Tauvry, 1700. 
Linsing, 1701. 
PauH, 1707. 
Barthold, 1717. 

S. Middlebeek, 17 19. 
Teichmeyer, 17 19. 
Gibson, 1726. 

(B) Alone; the umbilical blood being regarded as un- 
necessary or of minor importance, 
Moellenbroeck, 1672. 
Cosmopolita, 1686. 
Everardus, 1686. 
P. Stalpartius, 1687. 
Bierling, 1690. 

Case, 1696. (Case thought the embryo arose entirely 
out of the amniotic liquid like a precipitate from 
a clear solution.) 
Berger, 1702. 

These persons referred as their principal experi- 
mental basis to cases in which embryos had been 
born without umbilical cords, e.g. of those of: 
Rommelius, 1675 (in Velsch). 
Valentinius, 1 7 1 1 . 


(b) By the uterine milk or succum lacteo-chylosum. 

Mercklin, 1679. 
Drelincurtius, 1685. 
Bohnius, 1686. 
Zacchias, 1688. 
Tauvry, 1694. 
Franc, 1722. 
Dionis, 1724. 

III. That the embryo was nourished through the umbiHcal cord 

{a) By foetal blood (the circulations distinct). 

Arantius, 1595. 

Harvey, 1651. 

W. Needham, 1667. 

F. Hoffmann, 1681. (He proved the point by injection 
long before Hunter, who is stated by Cole to have been 
the first to demonstrate this.) 

Ruysch, 1 70 1. 

Snelle, 1705. 

Falconnet, 171 1. 

It is to be noted that Bierling, P. Stalpartius, Berger, 
Barthold, and Charleton, who supported the discon- 
tinuity theory of the circulations, were all upholders 
of the theory of foetal nourishment per os, so that their 
reasons for doing so were not those on account of 
which we agree with Hoffmann and Needham at the 
present time. 

{b) By maternal blood (the circulations continuous). 

Laurentius, 1600. 

de Marchette, 1656. 

Rallius, 1669. 

Muraltus, 1672. 

Blasius, 1677. 

Veslingius, 1677. 

Hamel, 1700. 

de Craan, 1703. 

Lang, 1704. 

van Home, 1707. 

Freind, 171 1. (Freind's Emmenologia deserves a special 
mention. He proved by a calculation that the amount 
of blood passing through the umbilical cord would be 
sufficient for the needs of the embryo. This is a parallel 
to Harvey's famous calculation about the circulation 
of the blood. He also quotes some experiments of 


Rayger and Gayant, who injected a blue dye into the 
foetal circulation and found it again in the maternal. 
Therefore he regards it as continuous.) 

Mery, 171 1. (Mery combated Falconnet's view of the 
separate circulations. He said that he had not himself 
tried Falconnet's experiment, but that some students 
had, and could not repeat it.) 

Aubert, 1 7 1 1 . (Narrative of a case in which the um- 
bilical cord had not been tied at the maternal end and 
the mother had nearly bled to death through it.) 

Nenterus, 17 14. 

Wedel, 1 71 7. 

Bellinger, 171 7. (Bellinger believed that the maternal 
blood was transformed by the embryonic thymus gland 
into proper nourishment for itself, after which it was 
secreted into the mouth by the salivary ducts and so 
went to form meconium without the necessity for de- 
glutination. Heister's comments on this extraordinary 
theory are worth reading. Perhaps Bellinger was in- 
debted to Tauvry for his idea of the importance of the 
thymus gland. Tauvry had drawn attention in 1700 
to its diminution after birth.) 

de Smidt, 17 18. 

Dionis, 1724. 

(c) By menstrual blood. 

Plempius, 1644. 

(d) By uterine milk. 

Ent, 1687. 

Camerarius, 17 14. {Opinio conciliatrix!) 

F. Hoffmann, 1718. 

{e) By the amniotic fluid. 

Vicarius, 1700. 
Goelicke, 1723. 

IV. That the embryo was nourished by pores in its skin. 

Deusingius, 1660. 
Nitzsch, 1 67 1. 
Stockhamer, 1682. 

This was suggested on the ground that in the earlier stages of 
development there is no umbilical cord. In 1684 St Romain argued 
against it on the ground that, if it were true, the embryo would 
dissolve in the amniotic liquid. 


During this period also there were continued disputes about the 
origin of the amniotic liquid, van Diemerbroeck and Verheyen con- 
sidered that it could not be the sweat of the embryo, for the embryo 
was always much too small to account for it, and, moreover, Tertre 
had described cases where the secundines had been formed with the 
membranes but in the absence of the embryo. Dionis affirmed that, 
whatever it was, it could not be urine, for urine will not keep good 
for nine days, a fortiori not for nine months. Drelincurtius put 
forward a theory that the embryo secreted it from its eyes and mouth 
by crying and salivating, while Bohn and Blancard derived it from 
the foetal breasts. Lang, Berger and Gofey criticised this notion 
without bringing forward anything constructive, and Gofey was in 
his turn annihilated by D. Hoffmann, who with Nenter and Konig 
supported the modern view, namely, that it was a transudation from 
the maternal blood-vessels in the decidua. The question was com- 
plicated further by the alleged discovery by Bidloo in 1 685 of glands 
in the umbilical cord, and by Vieussens in 1 705 of glands on the 
amniotic membrane. J. M. Hoffmann and Nicholas Hoboken sup- 
ported the view that these were the important structures. There the 
problem was left during the eighteenth century, various writers 
supporting different opinions from time to time, and it is still under 
discussion (see Section 22). 

Very early in the eighteenth century (1708) there appeared a 
work by G. E. Stahl, van Helmont's most famous follower, which 
struck the keynote of the whole century. Stahl's Theoria Medica Vera, 
divided as it was into Physiological and Pathological sections, be- 
longed in essence to the a priori school of Descartes and Gassendi. 
It differed from them profoundly, of course, for, instead of trying to 
explain all biological phenomena, including embryonic develop- 
ment, from mechanical first principles, it started out from first 
principles of a vitalistic order, and, having combined all the archaei 
into one informing soul, it sought to show how the facts could 
be perfectly well explained on this basis. But the spiritual kinship 
of Stahl with Descartes and Gassendi is due to an atmosphere 
which can only be called doctrinaire, and which was common 
to them all. Like the methodist school of Hellenistic medicine, 
they subordinated the data to a preconceived theory, during which 
process any awkward facts were liable to be rather submerged than 


In 1722 Antoine Maitre-Jan published his book on the embryology 
of the chick, the only one on this subject between Malpighi and 
Haller. It was an admirable treatise, illustrated with many drawings 
which, though not very beautiful, were as accurate as could be 
expected at the time. Perhaps its most remarkable characteristic 
is its almost complete freedom from all theory — Maitre-Jan says 
hardly a word about generation in general, and is far from putting 
forward a "system" in the usual eighteenth-century manner. He 
contents himself with the recital of the known facts, including those 
added by his own observations. He gives no references, and writes 
in an extremely modern and unaffected style. 

The only traces of theoretical presupposition which can be found 
in him are Cartesian, for he speaks of the activity of ferments in 
blood-formation. He is an epigenesist, and long before Brooks, he gives 
the right explanation of Malpighi's error, affirming that the hot 
Italian summer was responsible for some development in Malpighi's 
eggs before Malpighi examined them. Maitre-Jan's book must have 
been accessible both to Buffon and Haller, so it is difficult to see why 
they should have perpetuated Malpighi's mistake till nearly the end 
of the century. 

In technique, Maitre-Jan was pre-eminent. He was the first 
embryologist to make practical use of Boyle's suggestion regarding 
"distilled spirits of vinegar" for hardening the embryo so that it 
could be better dissected. He also used "weak spirits of vitriol"; 
after treating blastoderms with it, he said, "I saw with pleasure an 
infinity of little capillary vessels which had not appeared to be there 
before". He made a few chemical experiments also, noting that 
vinegar would coagulate egg-white, and estimating quantitatively 
the difference in oil-content of different yolks — though for this he 
gives no figures. 

His theory he relegated to an appendix entitled Objections sur 
la generation des animaux par de petits vers. There were sixteen of 
them, but the most cogent one was that, as little worms had been 
found under the microscope in pond-water, vinegar, and all kinds 
of liquids, there was no reason to suppose that those in the semen 
were in any essential way connected with generation. For his time, 
this argument was an excellent one, and was open to no demur 
save on the ground of filtration experiments which had not yet been 
made (see p. 215). 


About this time there was some controversy over the circulation 
of blood, the foramen ovale, etc., in the embryo. From 1700 to 1710, 
Tauvry and Mery were engaged in a polemic on this subject, and 
the latter also corresponded with Duverney, Silvestre and Buissiere 
in a controversy which recalls that of Laurentius and Petreus a 
hundred years before. Nicholls wrote later on the same subject. 
Daniel Tauvry was interesting, however, for other reasons. He was 
an epigenesist, and wrote vigorously against the view that the soul 
constructed during embryogeny a suitable home for itself. 

Nine years later two books appeared, which form very definite 
landmarks in the history of embryology. One was Martin Schurig's 
Embryologia, and the other the Elementa Chymiae of Hermann Boer- 

The former, however, gave to the world no new experiments or 
observations ; it was the first of what we should now call the typical 
"review" kind of publication. Schurig saw that he was living at 
the end of a great scientific movement following the Renaissance, 
and set himself accordingly for many years to compile large treatises 
on definite and restricted subjects, taking care to give all references 
with meticulous accuracy, and to omit no significant or insignificant 
work. His Spermatologia was the first to appear (in 1720), and it was 
followed in 1723 by Sialologia (on the saliva), Chylologia (1725), 
Muliebria (1729), Parthenologia (1729), Gynaecologia (1731) and Haema- 
tologia (1744). His Embryologia was the last but one of the series. In 
it he treated compendiously of all the theories which had been 
advanced about embryology during the immediately preceding two 
centuries, and his chapters on foetal nutrition and foetal respiration 
throw a flood of light on to the "intellectual climate" in which 
Harvey and Mayow worked, providing, as it were, the perishable back- 
ground of their immortal thoughts. Schurig's bibliography is a very 
striking part of his book, extending to sixteen pages, and including five 
hundred and sixty references; it was the first attempt of its kind. 

3-10. Boerhaave, Hamberger, Mazin 

Hermann Boerhaave was a more prominent figure, a Professor at 
Leyden for many years, and renowned for his encyclopaedic learning 
on all subjects remotely connected with medicine. His Elementa 
Chymiae, which became the standard chemical book of the whole 
period, demonstrates throughout the exceedingly wide outlook of its 


author, and contains in the second volume what must be regarded 
as the first detailed account of chemical embryology. I reproduce 
here the relevant passages in full because of their great interest. 
It will be noted that they are cast in the form of lecture addresses, 
as if they had been taken down direct from the lectures of the 
Professor, a fact which gives them a peculiar charm when it is 
remembered how many great men must have listened to them, among 
them Albrecht von Haller and Julien de la Mettrie. In considering 
what follows, it should be noted that Boerhaave's interest is bio- 
logical all the time, and that he does not treat the liquids of the egg, 
as nearly all the chemists before him had done, as substances of 
curious properties indeed, but quite remote from any question re- 
lating to the development of the embryo. Another interesting point 
is that he deals only with the white, and hardly mentions the yolk; 
this is perhaps to be explained by the Aristotelian theory that the 
embryo was formed out of the white, and only nourished by the 
yolk {ex alb fieri, ex luteo nutriri), a theory which was still alive, in 
spite of Harvey, in the first half of the eighteenth century. If this 
was what was at the bottom of Boerhaave's mind, then it is obvious 
that the egg-white would be to him the liquid inhabited more par- 
ticularly by the plastic force. This, then, is what he has to say about 
the biochemistry of the egg. 

Op. Chem. in Animalia. [Processus log.] The albumen of a fresh egg is not 
acid, nor alkaline, nor does it contain a fermented spirit. The white of a fresh 
egg, separated from the shell, the membranes, and the yolk, I enclose in 
clean glass vessels, and into each of these I pour different acids, and shake 
them up, mixing them, and no sign of ebullition appears however I treat 
them. Therefore I lay these vessels aside. Now in these other two vessels 
I have two fresh portions of albumen, and I mix with them in one case 
alkaline salt and in the other volatile alkali. You see they are quiet without 
any sign of effervescence. Now behold a remarkable thing, in this tall 
cylindrical vessel is half an ounce of the albumen of an egg and two drams 
of spirits of nitre, in this other vessel is half an ounce of egg-white, together 
with four and a half ounces of oil of tartar per deliquium both heated 
up to 92 degrees. Pray observe and behold, with one movement I pour 
the alkaline albumen into the acid albumen, with what fury they boil up, 
into what space they rarefy the mass, so that they stream out of the vessel 
although it is ten pints in size [decupli capace] . They have scarcely changed 
their colour. But when the effervescence has abated how suddenly they 
return to the limits of space occupied before. But now if more egg-white 
is heated to 100 degrees in a retort [cucurbita] an insipid water containing 


no spirit is given off. If egg-white is applied to the naked eye or naked 
nerve it does not give the smallest sense of pain, and scarcely affects the 
smell; nothing more inert and more insipid can be put on the tongue. It 
appears mucous and viscid to the touch, not at all penetrable. Hence in 
the fresh white of an egg there is no alkali or acid, or both together. It is 
indeed a thick, sticky, inert, and insipid liquor, yet from this truly vital 
liquid at a heat of 93 degrees within the space of 2 1 days the chick grows 
in the incubated egg from a tiny mass hardly weighing a hundredth of a 
grain into the perfect body of an animal, weighing an ounce or more. 
We have learnt therefore of a liquid distinct from all others, from which by 
inscrutable causes fibres, membranes, vessels, entrails, muscles, bones, 
cartilages, and all the other parts, tendons, ligaments, the beak, the claws, 
the feathers, and all the humours can be produced — and yet in this liquid 
we find softness, inertia, absence of acid, alkali, and spirit, and no ten- 
dency to effervesce. Indeed, if there were the slightest effervescence in it, 
it would certainly break the eggshell, therefore we see from how slow and 
inactive a mass all the solid and fluid parts of the chick are constructed. 
And yet this itself is rendered absolutely useless for forming the chick by 
greater heat. It scarcely bears 100 degrees with good effect but at a less 
temperature never brings forth a chick, for under 80 degrees will not 
suffice. But by a heat kept between these limits, there is brought about so 
marvellous an attenuation of the mucous inactivity that it can exhale a 
great part through the shell of the egg and the two membranes, the yolk 
and chalazae alone remaining along with the amniotic sac. For the yolk, 
the uterine placenta of the chick, takes little part in the nourishment. 
Meanwhile Malpighius has shown that this albumen is not a liquid of a 
homogeneous kind, as the blood-serum flowing through the vital vessels 
is, but that it is a structure composed of numerous membrane-like and 
distinct small saccules, filled with a liquid of their own, in the same way 
as in the vitreous humour of the eye. 

[Processus 1 1 1 .] Exploration of the egg-white with alcohol. In this trans- 
parent vessel is the albumen of an egg, and into it, as you perceive, I 
gently pour the purest alcohol, so that it descends down the sides of the 
vessel and reaches the albumen. I do this deliberately and with such 
solicitude that you may see the surface of the albumen which, touching 
the alcohol, holds it up, being immediately coagulated, while the lower 
part remains liquid and transparent. As I now gently shake them together, 
it appears evident that wherever the alcohol touches the albumen a con- 
cretion is formed. Behold now, while I shake them up thoroughly together, 
all the egg-white is coagulated. If alcohol previously warmed is employed 
in this experiment, the same result is brought about but more rapidly. 
It appears therefore that the purest vegetable spirits immediately coagulate 
the plastic and nutrient material. 

[Processus 112.] The fresh albumen of an egg is broken up by distillation. 
These fresh eggs have been cooked in pure water till they became hard. 
I now take the shining white, separating off all the other things, and break 
it up into small pieces. I put these, as you see, into a clean glass retort 


[cucurbita] and I duly cover it by fitting on an alembic and add a receiver. 
By the rules of the (chemical) art I place the whole retort in a bath of 
water and I apply to it successive degrees of fire until the whole bath is 
boiling. No vaporous streaks [^strid] of spirits are given off but simple 
water in dewy drops and this in incredible quantity, more than nine-tenths. 
I continue so with patience until by the heat of boiling water no more 
drops of this humour are given off. Then this water shows no trace of oil, 
salt, or spirit ; it is perfectly transparent and tasteless, except that it eventu- 
ally grows rather sour. It is odourless, save that towards the end it gives 
off a slight smell of burning. It shows absolutely no sign of the presence 
of any alkali, when I test it in every way, as you can see for yourselves ; 
nor does it reveal any trace of acid, when tried how you will. Here you 
see pounds of this water, but in the bottom of the now open retort see, 
I beg of you, how little substance remains. Behold, there are fragments 
contracted into a very small space in comparison with the former quantity. 
They are endowed with a golden yellow colour, especially where they have 
touched the glass, but yet they are transparent after the manner of coloured 
glass. When I take them out I find them very light, very hard, quite fragile, 
and breaking apart with a crack, smelling slightly of empyreuma, with 
a taste rather bitter from the fire, and without any flavour of alkali or 
acid. This is the first part of the analysis. Now I take these remaining 
fragments in a glass retort [retortam] in such a way that two-thirds remain 
over. I put the retort into a stove of sand, first arranging a large receiver. 
Then thoroughly luting all the joints I distil by successive grades of fire 
and finally by the highest which I call suppressionis. There ascends a spirit, 
running in streaks [^striatim] fat and oily, and at the same time, volatile 
salts of solid form everywhere on the walls of the vessel, rather plentiful 
in proportion to the dried fragments but small in proportion to the whole 
albumen before the water had been removed from it. Finally an oil appears 
besides the light golden material mixed with the first, black, thick, and 
pitchy. When by the extreme force of the fire this oil is finally driven forth, 
then the earth in the bottom, closely united with its most tenacious oil, 
swells up and is rarefied and rises right up to the neck of the retort so that 
had the retort been overfull it would have entered into the neck and 
clogged it up, even causing it to burst, with danger to the bystanders. The 
operation is to be continued till no more comes out. That first spirit, oily 
and fatty, is clearly alkaline by every test, as you may tell from the way it 
effervesces when acid is poured on it. If we rectify it we resolve it into 
an alkaline volatile salt, an oil, and inert foetid water. The salt fixed to 
the walls is completely alkaline, sharp, fiery, oily, and volatile; and the 
final oil is specially sharp, caustic, and foetid. The black earth which 
remains in the retort is shiny, light, thin, and fragile, foetid from the final 
empyreumatic oil, and soft because of it. If then it is burnt on an open 
fire, it leaves a little fixed earth which is white, insipid, tasteless, and 
odourless, from which scarcely any salt can be extracted, but only a very 
heavy dusty powder \^pollinein\. 

Cf. the dry distillation of egg-white by Pictet & Cramer in 1919. 


[Processus 113.] The fresh albumen of an egg will putrefy. Sound eggs kept 
at 70° for some days will become foetid and stink. . . .We have learnt then 
that this is the nature of the material which will shortly be changed into 
the structure, form, and all the parts of the animal body. Repose and a 
certain degree of heat produce that effect in that material. We observe 
therefore the spontaneous corruption and change of the material, and what 
is extremely remarkable, if an impregnated egg is warmed in an oven [in 
hypocaustis] to a heat of 92 degrees it employs these attenuated parts 
changed by such a heat to nourish, increase, and complete the chick for 
21 days. But in this chick nothing alkaline, foetid, or putrid is found, 
hence observe, O doctors [medici] , the remarkable manifestations of nature 
^by repose and a certain degree of heat a thick substance becomes thin, 
a viscous substance becomes liquid, an odourless substance becomes foetid, 
an insipid substance becomes sour and extremely acrid and bitter to the 
taste, a soothing substance becomes caustic, a non-alkali becomes alkaline, 
a latent oil becomes sweet and putrid. Let these results be compared with 
the observations of Marcellus Malpighius on the incubated egg, and we 
shall observe things which shall surprise us. I took care to investigate only 
the albumen of the egg first of all, separating the other parts off where 
possible, for the albumen alone forms the whole of the material which 
proceeds to feed [in pabulum] the embryo. The other constituents of the 
egg only assist in changing the albumen, so that when it is changed, it 
miay be applied to forming the structure of the chick. 

Boerhaave's treatment of these subjects has only to be compared 
with that of Joachim Beccher, who wrote in 1 703, to show how 
thoroughly modern in outlook it is. Beccher's Physica Subterranea 
contains a whole section devoted to the growth of the embryo, but 
it is extremely confused and very alchemical in its details. The 
advance made in the thirty years between Beccher and Boerhaave 
was immense, but, if the biochemistry of development advanced so 
fast, its biophysics was not far behind, as is shown by the work of 
G. E. Hamberger and J. B. Mazin. 

Hamberger's most important contributions, contained in his Physio- 
logia medica of 1 75 1 , were his quantitative observations on the water- 
content of the embryo and its growth-rate, in which he had no fore- 
runners, Hamberger showed "that there are much less solid parts 
in the foetus than in the adult. The cortical substance of the brain of 
an embryo loses 8694 parts in 10,000 on drying but in the adult it only 
loses 8096 and that of the cerebellum from 81 parts is reduced to 12. 
The maxillary glands of the embryo lose out of 10,000 parts 8469, the 
liver 8047, the pancreas 7863, the arteries 8278 and even the cartilages 
lose four-fifths of their weight, decreasing from 10,000 to 8149I ". The 


corresponding figures for the adult were: liver 7192, and heart 7836. 
These figures do not widely diflfer fi:-om those obtained in recent times. 

J. B, Mazin published his Conjecturae physico-medico-hydrostaticae de 
respiratione foetus in 1737 and his Tractatus medico-mechanica in 1742. 
In the first of these works Mazin supports what is essentially Mayow's 
theory of embryonic respiration, without, however, mentioning 
Mayow more than once. It had not been popular since 1700, though 
Pitcairn had defended it. Mazin put the liquids of eggs under an 
air-pump, and observing that air could be extracted from them 
affirmed that the air was hidden in them and that the embryo could 
therefore respire. He spoke of "aerial particles" in the amniotic 
liquid, and discussed the respiration of fishes in connection with this. 
The specific gravity of the embryo also interested him, and he did 
a great deal of calculation and experiment on it. His most interesting 
passage, perhaps, is that in which he mentions the "Eolipile" of 
the Alexandrians, the primitive form of the steam-engine, and says 
that just as the heat of the fire makes the water boil, so the heat of 
the viscera makes the amniotic liquid boil, giving off respirable 
vapours. The time-relations of this analogy are interesting, for in 
1705 Thomas Newcomen had succeeded in making a steam-engine 
which worked with considerable precision, and the question of steam- 
power was widely discussed. Possibly Mazin was acquainted with 
the Marquis of Worcester's Century of the Names and Scantlings oj 
Inventions, which had been published in 1663, and which had con- 
tained an aeolipile or "water-commanding machine". England was 
the centre of this movement and other countries employed English- 
men as engineers; Humphrey Potter, for instance, erected a steam- 
engine for pumping at a Hungarian mine in 1 720. 

As for the discovery of oxygen, it was near at hand, and Scheele in 
1 773 and Priestley in 1 774 were soon to supply the knowledge without 
which Mazin could not proceed further. 

In his second book, Mazin reported many quantitative observations 
on the specific gravity of the embryo. He found that it diminished 
as development proceeded, being to the amniotic liquid as 282 to 
274 in the fourth month and as 504 to 494 in the fifth month. 

Another instance of the way in which experimental physical ques- 
tions now began to come in is afforded by the work of Joseph Onymos, 
whose De Matura Foetu of 1 745 spoke of the specific gravity of the 
embryo at different stages of development. 


These writers, together with Haller himself, and J. C. Heffter 
who handled problems of embryonic rate of growth contribute to 
one of the best, because most quantitative, aspects of eighteenth- 
century embryology. 

3*11. Albrecht von Haller and his Contemporaries 

Boerhaave's greatest pupil was Albrecht von Haller. Like O. W. 
Holmes, at Harvard, Haller occupied a "settee" rather than a "chair", 
at Gottingen, and taught not only physiology but also medicine 
and surgery, botany, anatomy and pharmacology. Nor did he 
merely deal with so many subjects superficially; in each case he 
published what amounted to the best and most complete text-book 
up to then written. Haller was made Professor in 1736, and for 
many years worked at Gottingen, devoting much of his time to 
embryological researches, which, with those of his opponent Wolff, 
stand out as the greatest between Malpighi and von Baer. In 1 750 
he published a series of dissertations and short papers on all kinds 
of physiological subjects, which would have been the direct ancestors 
of the modern compilations of groups of experts, had they been more 
systematically arranged. The volume on generation repays some 
study. The contributions relevant to the present discussion had been 
written at various times during the previous seventy years, and may 
be summarised as follows : 

IV. Christopher Sturmius, De plantarum animaliumque generatione. 
(First published 1687.) In this paper Sturmius argues on 
behalf of the preformation theory "which in our times 
does not lack supporters", quoting Perrault, Harvey and 
Descartes. He contents himself with countering arguments 
which had been urged against it, as, {a) spontaneous 
generation, {b) annual recurrence of plants, {c) insect 
metamorphosis, {d) generation without copulation. 
V. Rudolf Jacob Camerarius, Specimen experimentorum physiologico- 
therapeuticorum circa generationem hominis et animalium. The 
most interesting thing about this is that Camerarius 
mentions the observations of D. Seiller, a sculptor, who 
had ascertained that the body is five times the size of the 
head in the embryo but seven and a half times the size of it 
in the adult. This is in the direct line between Leonardo 
and Scammon. 

SECT. 3] 



XV. Philip Gravel, De Super Joetatione. (First published 1738.) 

XVIII. Adam Brendel, De embryone in ovulo ante conceptum praeexistante. 
(First published 1703.) Brendel "stands for the Graafian 
hypothesis''. Unfortunately, he was also a preformationist 
and believed that every limb, organ, and function existed 
not potentially but actually in the unfertilised Qgg before 
its passage down the Fallopian tube. 

XXII. Camillus Falconnet, Non est fetui sanguis maternus alimento. 
(First published 171 1.) This is the first of the French 
contributions to the book; they are all very markedly 
shorter than the German ones and much less heavily 
ornamented with irrelevant quotations. Falconnet is con- 
cerned to prove that the maternal and foetal circulations 
are separate, and he describes in an admirably concise 
manner an experiment in which he bled a female dog to 
death, after which, opening the uterus, he discovered that 
the embryonic blood-vessels were full of blood although 
those of the mother had none in at all. Arantius was there- 
fore justified. Falconnet was soon confirmed by Nunn. 

XXIII. Jean de Diest's Sui Sanguinis solus opifex fetus est (first 
published 1735) was written to prove a similar point. He 
refers to the experiment of Falconnet and the injections 
of F. Hoffmann, and criticises Cowper's experiment in 
which mercury had been injected into the umbilical vessels 
and found in the maternal circulation, on the grounds that 
mercury is so "tenuous and voluble" that it might pass 
where blood could not pass normally. He also objects to 
the view that the foetus is nourished by the amniotic liquid. 

XXIV. Francis David Herissant, Secundinae fetui pulmonis praestant 
officia, et sanguine materno fetum non alitur. (First published in 
1 741.) An excellent paper, in which the respiratory function 
of the placenta is proved by the observation that the foetal 
blood-vessel leading to the placenta is always full of dark 
venous blood, while that leading away fi-om the placenta 
is light and arterial [floridiori coccineoque colore, ut ipsemet 
observavi]. Herissant adduces also the cases of acephalic 
monsters, such as that of Brady, which could not possibly 
have drunk up any amniotic fluid, and yet were fully formed 


in all other respects. He concludes that the umbilical cord 
serves for respiration and nutrition. 

XXV. After these three French workers, there is a great drop to 
Johannes Zeller, whose Infanticidas non absolvit nee a tortura 
liberal pulmonum infantis in aqua subsidentia (first published 

1 691) is a long-winded discussion of the floating lung test 
in forensic medicine. His memory deserves a word of obloquy 
for his vigorous insistence upon torture and death for in- 
fanticide even during puerperal insanity. Perhaps it was 
Zeller who called forth the noble answer of de la Mettrie 
to this inhumanity in his Man a Machine. 

XXVI. Zeller's De Vila Humana ex June pendenle (first published 

1692) is no better, though at the time, perhaps because 
of its striking title, it was famous. It deals with the ligation 
of the umbilical cord at birth. 

This completes the list of the papers published by Haller in his 
1750 collection. He retired from the Gottingen chair three years 
later, and in 1757 the first volume of his Elemenla Physiologiae was 
published, probably the greatest text-book of physiology ever written. 
It appeared only by slow degrees, so that it was not until 1766 that 
the embryological section was available. This volume contains 
a discussion of a mass of literature, most of which had arisen 
during the preceding twenty-five years, for, although many of the 
names mentioned by Haller occur also in Schurig, yet many are 
quite new. 

Haller himself published in 1 767 a volume of his collected papers 
on embryology, most of which were concerned with the developing 
heart of the chick, which he worked out very thoroughly, in collabora- 
tion with Kuhlemann. (Kuhlemann had already done for the 
sheep what Harvey had done for the doe.) He made a beginning 
with the quantitative description of embryogeny, and one of his 
tables showing the changing lengths of the bones is reproduced here- 
with (Fig. 10). He was a convinced preformationist, a fact which was 
largely due to his researches on the hen's egg, where he observed that 
the yolk had a much more intimate connection with the embryo 
than had previously been supposed. Since the whole yolk was part of 
the embryo, as it were, the preformation theory seemed to him to 
fit the facts better than epigenesis. 












Quart us 






l| MUS 



MUS Se- 









1 8- prox. 










+4. ptox. 





















1 1 



43. prox 










3 0. prox. 























Fig. 10. Facsimile of a table in A. von Haller's Elementa Physiologiae of 1766, containing some of his 
observations on the growth in length and weight of embryonic bones in the chick. 


Haller went further than Schurig, in that he usually gave an opinion 
of his own after summarising those of other people, but his views were 
by no means always enlightened, and the atmosphere of Buffon is, 
on the whole, more congenial to us than that of Haller. Haller, 
for example, believed that the amniotic liquid had nutritious pro- 
perties, and that the nutrition of the embryo in mammalia was 
accomplished first of^ all per os and afterwards per umbilicum. He denied 
that the placenta had any respiratory function, and, indeed, his 
whole teaching on respiration was retrograde. He mentions, how- 
ever, an experiment of Nicolas Lemery's, in which it had been 
found that indigo would penetrate the shell of a developing hen's 
tgg from the outside. Consequently, air might do so too, and 
Vallisneri had shown that, if an egg was placed in boiled water under 
an air-pump, the air inside would rush out through the shell and 
appear in the form of bubbles. 

Haller was much more progressive in holding the origin of the 
amniotic liquid (according to him a subject of extraordinary diffi- 
culty — " solutionem non promittam'") to be a transudation from the 
maternal blood-vessels. He followed Noortwyck in asserting the 
separateness of the maternal and foetal circulations in mammalia. 
He opposed the existence of eggs in vivipara — "We may conclude 
from all this", he said, "that the ovarian vesicles are not eggs and 
that they do not contain the rudiments of the new animal". But he 
accepted it in the restricted sense that the embryonic membranes 
resembled an egg, thus: "If we call an egg a hollow membranous 
pocket full of a humour in which the embryo swims, we may admit 
the opinion of the older authors who derive all animals from eggs 
with the exception of the tiny simple animals of which we have 
already spoken. It was in this sense that Aristotle and Empedocles 
before him, said that even trees were oviparous. This has also been 
confirmed by the experiments of Harvey on insects, fishes, birds, and 

Haller's most original work was in connection with the growth- 
rate of the embryo ; here he struck out, for once, into entirely new 
country. "The growth of the embryo in the uterus of the mother is 
almost unbelieveably rapid. We do not know what its size is at the 
moment of its formation, but it is certainly so small that it cannot 
be seen even with the aid of the best microscopes, and it reaches in 
nine months the weight of ten or twelve pounds. In order to clear 


up this speculation, let us examine the growth of the chick in the 
egg. We cannot in this case either measure its size at the moment 
when the egg is put to incubate but it cannot be more than j^ in. 
long, for if it were, it would be visible, and yet 25 days later it is 
4 ins, long. Its relation is therefore as 64 to 64 millions or i to i 
million. This growth takes place in a singular manner, it is very rapid 
in the beginning and continually diminishes in speed. The growth 
on the first day is from i to gi^^ and what Swammerdam calls a 
worm grows in one day from one-twentieth or one-thirtieth of a 
grain to seven grains, i.e. it increases its weight by 140 or 240 times. 
On the second day the growth of the chick is from i to 5, on the third 
day, from i to not quite 4, on the fifth day from i to something 
less than 3. Then from the sixth to the twelfth day, the growth each 
day is hardly from 4 to 5, and on the twenty-first day it is about 
from 5 to 6. After the chick has hatched, it grows each day for the 
first 40 days at an approximately constant rate, from 20 to 2 1 on each 
day. The increase of the first twenty-four hours is therefore in relation 
to that of the last twenty-four hours as 546I to 5 or 145 to i. Now 
as the total increase in weight in the egg is to that of the whole 
growth period (up to the adult) as 2 to 24 ozs., all the post-embryonic 
growth is as i to 12, i.e. it is to the growth of one day alone early 
in incubation as i to 7|.. . .The growth of man, like that of the 
chick, decreases in rapidity as it advances. Let us suppose that a 
man, at the instant of conception, weighs a hundred-thousandth of 
a grain and that a one-month old embryo weighs 30 grains; then 
the man will have acquired in that time more than 300,000 times 
the weight that he had to begin with. But if a foetus of the second 
month weighs 3 ozs. as it approximately does, he will only now have 
acquired 48 times the weight he had at the beginning of the period. 
This is a prodigious decrease in speed, and at the end of the ninth 
month he will not weigh more than about 105 ozs., which is not 
more than an average increase of 15 per month. A child three years 
old is about half the size of an adult. If then the adult weighs 
2250 ozs. the three-year old child only weighs 281 ozs., which is an 
eighth of the adult weight. Now from birth to 3 years he will grow 
from 105 to 281 or as 5 to 14, but in the following 22 years he will 
only accumulate 2250 ozs. or eight times what he had at 3 years. 
The growth of a man will therefore be in the first month of intra- 
uterine life as I to 300,000, in the second as i to 48, in each of the 

N E I 13 


others as i to 15. In the first 3 years of extra-uterine life his growth 
will be from 164 to 281 and in the succeeding 22 years from 281 to 
384, and the growth of the first month to the last will be as 300,000 
to ^% or 136,800,000 to 28, or 4,885,717 to i. The whole growth of 
man will consequently be as 108,000,000 to i." 

In spite of the rather unfamiliar language in which these facts are 
described, and the theory of the growth of the heart which Haller 
subsequently put forth to explain them, they remain fundamental 
to embryology. Their quantitative tone is indeed remarkably modern. 
In my opinion, when all the voluminous writings of Haller are care- 
fully searched through, nothing more progressive and valuable than 
these figures can be found. Haller and Hamberger stand thus 
between Leonardo on the one hand and Minot and Brody on the 
other. That they stood so much alone is only another indication of 
the extraordinary reluctance with which the men of past generations 
assented to the truth contained in Robert Mayer's immortal words, 
"Eine einzige Zahl hat mehr wahren und bleibenden Wert als eine 
kostbare Bibliothek von Hypothesen". 

Of development as a whole, Haller spoke thus, " In the body of the 
animal therefore, no part is made before any other part, but all are 
formed at the same time. If certain authors have said that the animal 
begins to be formed by the backbone, by the brain, or by the heart, if 
Galen taught that it was the liver which was first formed, if others have 
said that it was the belly and the head, or the spinal marrow with the 
brain, adding that these parts make others in turn, I think that all these 
authors only meant that the heart and the brain or whatever organ 
it was, were visible when none of the other parts yet were, and that 
certain parts of the embryonic body are well enough developed in the 
first few days to be seen while others are not so until the latter part of 
development; and others again not till after birth, such as the beard 
in man, the antlers in the stag, the breasts and the second set of teeth. 
If Harvey thought he descried an epigenetic development, it was 
because he saw first a little cloud, then the rudiments of the head, with 
the eyes bigger than the whole body, and little by little the viscera 
being formed. If one compares his description with mine, one will see 
that his description of the development of the deer corresponds 
exactly with mine of the development of the chick. If, more than 
twenty years ago, before I had made many observations upon eggs 
and the females of quadrupeds I employed this reasoning to prove 


that there is a great difference between the foetus and the perfect 
animal, and if I said that in the animal at the moment of conception 
one does not find the same parts as in the perfect animal, I have 
realised abundantly since then that all I said against preformation 
really went to support it". The reasons for this change of opinion 
become no clearer as Haller's writings are more assiduously read, 
and, as Dareste says, why he should have made it, will always 
remain a mystery. 

The emboitement aspect of preformation presented no difficulties to 
Haller. "It follows", he said, speaking of the generation of Volvox, 
"that the ovary of an ancestress will contain not only her daughter, 
but also her granddaughter, her great-granddaughter and her great- 
great-granddaughter, and if it is once proved that an ovary can 
contain many generations, there is no absurdity in saying that it 
contains them all," 

The following passage is interesting. "We must proceed to say 
what is the efficient cause of the beautiful machine which we call 
an animal. First of all let us not attribute it to chance, as Ofrai 
[is this Julien Offi-ay de la Mettrie? Haller had a habit of using 
Christian names, e,g, Turberville for J. T. Needham] would have 
us do, for although he pretends that all animals come from earth, 
he is not attached to the ancient opinion, and nobody now believes 
what Aelian says, namely that frogs are born from mud. . . , Vallisneri 
has found the fathers and mothers of the little worms in galls, a quest 
of which Redi despaired, and Redi in his turn has made with exacti- 
tude and precision those experiments which Bonannus, Triumphet, 
and Honoratus Faber had only sketched out imperfectly. Moreover, 
no seed, no clover. . . . This was the received opinion but in our century 
a proscribed notion has been revivified and some great men have 
pretended that there are little animals which are engendered by an 
equivocal generation, without father and mother, and that all the 
viscera and all the parts of these animals do not exist together, but 
that the nobler parts are formed first by epigenesis and that then 
the others are formed little by little afterwards." This is an admirable 
illustration of how spontaneous generation and epigenesis were bound 
up together, "M. Needham", Haller goes on to say, "does not admit 
an equivocal generation but he does admit epigenesis, and a corporeal 
non-intelligent force, which constructs a body from a tiny little germ 
furnishing the necessary matter for it. He says that there are only 



the primitive germs which were made at the original creation and 
that germs organised Hke animals do by no means pre-exist, for if 
they did, molae uterinae, encysted tumours, and the like, could not 
come into being." Haller then goes on to describe Needham's 
experiments with meat broths, etc., and objects to his "system", 
largely on the ground that "blind forces without any intelligence 
could hardly be able to form animals for ends foreseen and ready 
to take their places in the scheme of beings". He considers that 
Needham's theories are completely disproved by experiments such 
as those of Spallanzani, though, curiously enough, he does not quote 
the latter author in this connection. I shall return to this later. 

"Nobody", he goes on to say, "has upheld epigenesis more than 
M. Wolff, who has undertaken an examination to demonstrate that 
plants and animals are formed without a mould out of matter by a 
certain constant force which he calls 'essential' [in his Theoria 
Generationis] .... I have indeed seen many of the phenomena which 
he describes, and it is certain that the heart seems to be formed out 
of a congealed humour and that the whole animal appears to have 
the same consistency. But it does not follow that because this 
primitive glue which is to take on the shape of the animal does not 
appear to possess its structure and all its parts, it has not effectively 
got them. I have often given greater solidity to this jelly by the use 
merely of spirits of wine and by this means I saw that what had 
appeared to me to be a homogeneous jelly was composed of fibres, 
vessels, and viscera. Now surely nobody will say that the vis 
essentialis of the spirit of wine gave an organic structure to an un- 
formed matter, on the contrary it is rather in the removal of trans- 
parency and the accession of greater firmness to the extremities, as 
well as the making of a more obvious boundary to the contour of 
a viscus that one could see the structure of a cellular tissue, which 
was ready to be formed but which the transparency had previously 
hidden and the wetness not allowed to be circumscribed by lines. . . . 
Finally, to cut a long story short, why does this vis essentialis, 
which is one only, form always and in the same places the parts of 
an animal which are so different, and always upon the same model, 
if inorganic matter is susceptible of changes and is capable of taking 
all sorts of forms? Why should the material coming from a hen 
always give rise to a chicken, and that from a peacock give rise to 
a peacock? To these questions no answer is given." This was the 


case because Wolff was not a theorist, but rather an experimentalist; 
his writings are marked by their abstention from the discussion of 
speculative points. The above passage is very interesting. It reminds 
us of the great difficulties with which the embryologists of this epoch 
had to contend. Serial section cutting was unknown, the staining 
of thin layers and reconstruction were unheard of; even the hardening 
of the soft embryonic tissues was only just discovered, as is indicated 
by Haller above. Hertwig has excellently discussed the advances in 
embryological technique which took place during this and the fol- 
lowing century. It is true that dyes were beginning to be used, as 
some instances already given demonstrate, and as is seen from the use 
of madder in the staining of bones, which began about this time, and 
was later much used by the Hunters. Heertodt's Crocologia is im- 
portant in this connection. Heertodt, by injecting saffron into the 
maternal circulation, found it afterwards in the amniotic fluid, and 
his experiment was cited by Haller in support of that theory of the 
origin of the liquid. But the most important advance in technique 
was the progress in artificial incubation. The art, though lost through- 
out the Middle Ages and the seventeenth century, was now to be 

During this period much work was done on it. As far back as 
1 600, de Serres had mentioned some experiments of this nature, but 
they were not successful. "The chicks", he said, "were usually born 
deformed, defective or having too many legs, wings, or heads, nature 
being inimitable by art." Birch, in his History of the Royal Society, also 
refers to it. "Sir Christopher Heydon [a relative of Digby's Sir 
John?] together with Drebell, long since in the Minories hatched 
several hundred eggs but it had this effect, that most of the chickens 
produced that way were lame and defective in some part or other." 
Antonelli states that similar trials were made at the court of the 
Grand-duke Ferdinand II at Florence about 1644, Thomas Bartho- 
linus gives a like account with reference to the contemporary court 
of King Christian IV of Denmark, and Poggendorff and Antinori 
relate that the Accademia d. Cimento, inspired by Paolo del Buono, 
made trial of artificial incubation between 1651 and 1667. 

But the most famous of all the attempts to make artificial as suc- 
cessful as natural incubation, were those of Reaumur, whose book 
De I' art defaire eclore les poulets of 1749 achieved a wide renown. He 
devotes many chapters to a detailed description of incubators of very 


various kinds : but he nowhere gives any indication of his percentage 
hatch. It was probably low. He speaks also of the ^^funestes effets'^ 
of the vapours of the dung on the developing embryos, without, how- 
ever, furnishing any foundation for an exact teratology. In the second 
volume he describes those experiments on the preservation of eggs 
by varnishing them, which caught the imagination of Maupertuis 
and were held up to an immortal but by no means deserved ridicule 
by Voltaire in his Akakia. For the details of this amusing but 
irrelevant issue see Miall and Lytton Strachey. 

After Reaumur, there were numerous continuations of the kind of 
work which he had done, in particular by Thevenot, La Boulaye, 
Nelli, Porta and Cedernhielm. Much the most interesting of these 
was the work of Beguelin, who attempted to incubate eggs with 
part of the shell removed so as to form a round window. He was not, 
however, successful in the carrying out of this very modern idea. 
Probably the most peculiar investigation made in this field at this 
time was that of Achard, who is mentioned in a passage of Bonnet's. 
"Reaumur did not suspect in 1749", says Bonnet, "that someday 
one would try to substitute the action of the electric fluid for his 
borrowed heat. This beautiful invention was reserved for M. Achard 
of the Prussian Academy who excels as an experimentalist. He has 
not so far succeeded in actually hatching a chick by means of so new 
a process, but he has had one develop up to the eighth day, when 
an unfortunate accident deranged his electrical apparatus." Bonnet 
goes on to say that this substitution of electricity for heat gives him 
hope that by electrical means an artificial fertilisation will one day 
become possible. 

The references to these experiments and to those of many minor 
investigators will be found in Haller. By the beginning of the nine- 
teenth century a great mass of literature had developed on the 
subject, and it had become possible to hatch out eggs more or less 
successfully from furnaces, though the losses were still great. Early 
in the nineteenth century Bonnemain and Jouard referred to the 
large number of monsters produced, and in 1809 Paris wrote, 
"During the period that I was at College, the late Sir Busick Har- 
wood, the ingenious Professor of Anatomy in the University of 
Cambridge, frequently attempted to develope eggs by the heat of 
his hotbed, but he only raised monsters, a result which he attributed 
to the unsteady application of the heat". 



This is the most convenient place to mention theological embryo- 
logy once again. Its place in the eighteenth century was small, and 
in the nineteenth, with the recognition that whatever the soul is, it 
is not a phenomenon, it altogether disappeared from serious general 
discussion. F. E. Cangiamilla's Embryologia Sacra, however, ran through 
several editions between 1700 and 1775. Cangiamilla {Panorm. 
Eccl. Can. Theol. et in toto Sicil. regno contra haereticam pravitatem 
Inquisitore provinciali) deals very frilly with the time of animation, 
quoting a host of writers such as St Gelasius, St Anselm, Hugh of 
St Victor and Pico della Mirandola. His mind retains a quite 
mediaeval conformation, as the following curious passage illustrates : 
'^ Quot non foetus abortivos ex ignorantia obstetricum et matrum excipit 
lafrina, quorum anima, si Baptismate non fraudaretur, Deum in aeternam 
videret, esset decentius tumulandum! " His instructions for the baptism 
of monsters are also very odd. But theological embryology probably 
reached its climax in the report of the Doctors of Divinity at the 
Sorbonne on March 30, 1733, in which intra-uterine baptism by 
means of a syringe was solemnly recommended. This is included 
in Deventer's book, and has been referred to by Sterne and Spencer. 
For other aspects of these tracts of thought see Nicholls and his 
anonymous antagonist. But Cangiamilla and his colleagues — Gerike, 
Kaltschmied, etc. — are only of decorative importance to our present 
theme, and for fuller information regarding them, reference must be 
made to the treatise of Witovski. It is interesting to note that as 
late as 1913, 182 days was fixed as "perfection-time", whatever that 
may be, by Moriani. 

3*12. Ovism and Animalculism 

We must now return to the beginning of the century in order to 
pick up the thread of the main trend of thought. By 1720 the theory 
of preformation was thoroughly established, not only on the erroneous 
grounds put forward by Malpighi and Swammerdam, but on the 
experiments of Andry, Hartsoeker, Dalenpatius and Gautier, who 
all asserted that they had seen exceedingly minute forms of men, 
with arms, heads, and legs complete, inside the spermatozoa under 
the microscope. Gautier went so far as to say that he had seen a 
microscopic horse in the semen of a horse (he gave a plate of it) 
and a similar animalcule with very large ears in the semen of a 
donkey; finally, he described minute cocks in the semen of a cock. 


Haller remarks gently that he has searched for these phenomena in 
vain. Vallisneri asserted the same kind of thing about the mammahan 
ovum, though he admitted that, in spite of long searching, he had 
never seen one. Besides the main distinction between prefer mationists 
and epigenesists, then, there arose a division among the former 
group, so that the ovists regarded all embryos as being produced 
from smaller embryos in the unfertilised eggs, while 
the animalculists regarded all embryos as being 
produced from the smaller embryos provided by 
the male in his spermatozoa. The animalculists 
thus afforded a singular example of a return to 
the ancient theory mentioned by Aeschylus in the 
Oresteia (see p. 65). Their most conspicuous ex- 
ample was Nicholas Andry, who pictured each 
c^gg as being arranged like the Cavorite sphere in 
which H. G. Wells' explorers made their way to the 
moon, i.e. with one trap-door. The spermatozoa, 
like so many minute men, all tried to occupy an 
egg, but as there were far fewer eggs than sperma- 
tozoa, there were, when all was over, only a few 
happy animalcules who had been lucky enough 
to find an empty egg, climb in, and lock the door 
behind them. 

The whole controversy was intimately bound 
up with the question of spontaneous generation, 
for, whatever the case might be in the higher 
animals, if it were true that the lower ones could arise de novo 
out of slime, mud, or meat infusion, for instance, then their parts 
at least must have been made by epigenesis, and not in any other 
way, for it could hardly be held that a homogeneous infusion had 
any structure of that kind. And if epigenesis could occur in the lower 
animals, then the thin end of the wedge had been driven in, and it 
might occur among the higher ones as well. It was in this way that 
the spontaneous generation controversy came to have a peculiar 
importance for embryology in the eighteenth century. Driesch has 
essayed to make the generalisation that all the supporters of epigenesis 
were vitalistic in their tendencies, while those who adhered to the 
preformation theory were not. But there are too many exceptions 
to this rule to make it of any use. In so far as there is truth in it. 

Fig. 1 1 . Hartsoeker's 
drawing of a human 


it doubtless arose from the fact that, in epigenesis, a continual pro- 
duction of new organs and new relationships between organs already 
formed would seem to require an immanent formative force of some 
kind, such as the vis essentialis of Wolff; while, on the preformation 
hypothesis, where embryogeny was little more than a swelling up 
of parts already there, it could be explained as simply as nutrition. 
The failure of the "short-cut" mechanical philosophers such as 
Gassendi and Descartes thus led to preformationism just as much as 
to epigenesis. A remark of Cheyne's throws much light on this 
question, for in 17 15 he wrote, unconsciously following Gassendi's 
line of thought, "If animals and vegetables cannot be produced 
from matter and motion (and I have clearly proved that they can- 
not), they must of necessity have existed from all eternity". Pre- 
formationism was thus the only resource if the universal jurisdiction 
of the mechanical theory of the world was to be retained. Stahl and, 
later, Wolff, saw no point in retaining it, and carefully joined 
together what Descartes had, with equal care, put asunder. 

The original discoveries of de Graaf and Stensen were extended 
by Tauvry in 1690 to the tortoise, and by Lorenzini in 1678 to the 
Torpedo', so that the eighteenth century began with an excellent 
basis for ovistic preformationism. The greatest names associated with 
this school were Swammerdam, Malpighi, Bonnet, v. Haller, Winslow, 
Vallisneri, Ruysch and Spallanzani. But there were many others, 
some of whom did valuable work, such as Bianchi, Sterre, Teichmeyer, 
Weygand, Perrault, Vercelloni, Vidussi, Bussiere, Fizes and Cosch- 
witz. The treatises of Imbert and Plonquet were written from this 
point of view, as was the bright little dialogue of de Houpeville. 
J. B. du Hamel asserted that he could see the chick embryo in the 
Ggg before fertilisation, and Jacobaeus made a like affirmation in the 
case of the frog. 

On the other side, that of animalculistic preformationism, the 
contestants were fewer. Their greatest names were Leeuwenhoek, 
Hartsoeker, Leibnitz and the cardinal de Pohgnac. In England 
the physicians Keil and Cheque supported this position, in France 
Geofroi and the obstetrician la Motte, in Germany Withof and 
Ludwig, and in Belgium Lieutaud. De Superville wrote in favour 
of it in the Philosophical Transactions of the Royal Society, and an anony- 
mous Swedish work of some fame supported it. To the argument 
of Vallisneri that the existence of so many animalcules must be an 


illusion, since Nature could hardly be so prodigal, the animalculists 
retorted by instancing such observations as that of Baster, who had 
taken the trouble to count the eggs of a crab and had found that 
they amounted to 12,444. James Cooke later elaborated a theory 
of a world of the unborn to which the spermatozoa could retire 
between each attempt to find a uterus in which they could develop — 
this avoided Vallisneri's argument. "All those other attending 
Animalcula, except that single one that is then conceived, evaporate 
away, and return back into the Atmosphere again, whence it is very 
likely they immediately proceeded; into the open Air, I say, the 
common Receptacle of all such disengaged minute sublunary bodies; 
and do there circulate about with other Semina, where, perhaps, 
they do not absolutely die, but live a latent life, in an insensible or 
dormant state, like Swallows in Winter, lying quite still like a stopped 
Watch when let down, till they are received afresh into some other 
Male body of the proper kind, to be again set on Motion, and ejected 
again in Coition as before, to run a fresh chance for a lucky Con- 
ception ; for it is very hard to conceive that Nature is so idly luxurious 
of Seeds thus only to destroy them, and to make Myriads of them 
subservient to but a single one." But Cooke's attractive hypothesis, 
published in 1762, came too late, as Punnett says, to save the 

On the experimental side. Garden and Bourguet came forward 
with descriptions of little men inside the animalcules, thus confirming 
the work of Gautier and Hartsoeker. It is fair to add, however, that 
Garden held quite enlightened views of the mutual necessity of egg 
and spermatozoon. La Motte maintained that the egg (which he 
identified with the Graafian follicle) was too big to go down the 
Fallopian tube, and Sbaragli, another writer on the animalculist 
side, agreed with him. 

Leeuwenhoek, it must be admitted, indulged in assertions no less 
fantastic than those of his followers. He said there were spermatic 
animalcules of both sexes, as one could see by a slight difference near 
their tails, that they copulated, that the females became pregnant 
and gave birth to little animalcules, that young and feeble ones could 
be seen, that they shed their skins, and, finally, that some had been 
observed with two heads. Haller, who made good use, on the whole, 
of his strong vein of scepticism, characterised all these remarks as 
"only conjectures". (See Fig. 12.) 

SECT. 3] 



As for the supporters of epigenesis, they were few, but they 
included Descartes, de Maupertuis, Antoine Maitre-Jan and John 
Turberville Needham. Von Haller affords some evidence against the 
identification of epigenesis with vitaHsm and preformation with 
mechanism, for he says, "Various authors have taught that the parts 
of the human body are formed by a mechanism depending on general 
laws (i.e. laws not simply of biological jurisdiction) or by the virtue 
of some ferment, or by rest and cold making crusts out of the different 
juices, or in other ways. All these (mechanical) systems have some 
resemblance to that of M. Wolff". Haller also speaks always of 
Wolff's vis essentialis as "blind". Minor writers on the epigenetic side 
were Tauvry, Welsh, 
Dartiguelongue, Bou- 
ger, Drelincurtius and 
Mazin. After 1 750 
C. F. Wolff brought 
an abiding victory to 
their opinion. 

Some maintained a 
quite independent po- 
sition, such as Buffon, 
who welded together 
an epigenetic theory 

of fertilisation with a ^^S- 12. Dalenpatius' drawings of human spermatozoa. 

preformationist theory of embryogeny. Pascal (not the great Jan- 
senist) put forward the chemical view that fertilisation consisted of 
a combination between the acid semen of the male and the "lixivious " 
semen of the female, no doubt because in chemistry acids were 
regarded as male and alkalies female. Claude Perrault and Connor 
also suggested that the formation of the embryo was a fermentation 
set up in the egg by the spermatic animalcule. In this they were 
following the example of van Helmont, who had originally suggested 
such a theory. In 1 763 Jacobi discovered how to fertilise fish eggs 
with milt; a practical matter which had a good deal of influence on 
biological theory. Launai alone still held to the Aristotelian con- 
ception of form and matter. 

There is no need here to do more than glance at the spontaneous 
generation controversy itself, for it has always been well known in 
the history of biology, especially in connection with the subsequent 


work of Pasteur. J. T. Needham's books, New Microscopical Dis- 
coveries of 1745 and Observations upon the generation, composition, and 
decomposition of animal and vegetable substances of 1 750, exercised a con- 
siderable influence. They were written after the French fashion 
(Needham had been educated at Douai) very concisely, and with 
some brilliance of style, and it is hardly true to say, as Radl does, that 
their experimental foundation was meagre. That it was inadequate 
was proved definitely as events turned out by Spallanzani. De 
Kruif 's account of the controversy is false and misleading, especially 
in its estimate of Needham who is much more truly described in 
the words of Louis Pasteur (see also Prescott). 

Needham's case rested upon the statement that, if meat broth was 
placed in a sealed vessel and heated to a high temperature so that 
all life was destroyed in it, it would yet be found to be swarming 
some days later with microscopical animals. All depended, therefore, 
upon the sureness with which the vessel had been sealed and the 
efficacy of the heat employed to kill all the animalcules initially 
present, and, in the ensuing controversy, Needham lost to Spallanzani 
entirely on a question of technique. It may be remarked here, with- 
out irrelevance, that the problem is still unsolved; for all that was 
proved by the experiments of Spallanzani was that animals the size 
of rotifers and protozoa do not originate spontaneously from broth, 
and all that was proved by those of Pasteur was that organisms the 
size of bacteria do not originate de novo in that way. The knowledge 
which we have acquired in recent years of filter-passing organisms, 
such as the mosaic disease of the tobacco-plant, and phenomena such 
as the bacteriophage of Twort and d'Herelle, has reopened the whole 
matter, so that of the region between, for example, the semi-living 
particles of the bacteriophage (lO"^^ gram) and the larger sized 
colloidal aggregates (io~^^ gram) we know absolutely nothing. The 
dogmatism with which the biologists of the early twentieth century 
asserted the statement omne vivum ex vivo was therefore, like most 
dogmatisms, ill-timed. 

But to dwell further on this would be a digression. The important 
point was that Spallanzani's victory was a victory not only for 
those who disbelieved in spontaneous generation, but also for those 
who believed in the preformation theory of embryogeny. By 
1 786, indeed, that viewpoint was so orthodox that Senebier, in his 
introduction to an edition of Spallanzani's book on the generation 


of animals and plants, could treat the epigenesists as no better than 

Spallanzani's views on embryology were largely drawn from his 
study of the development of the frog's egg. Here he went far beyond 
Bosius, but, in spite of many careful observations, he thought he saw 
the embryo already present in the unfertilised ova. This led him to 
claim that amphibia ought to be numbered among viviparous 
animals. His principal step forward was his recognition of the 
semen as the actual agent in fertilisation on definite experimental 
grounds — the narrative of his artificial insemination of a bitch 
is too famous to quote; he said it gave him more intellectual satis- 
faction than any other experiment he had ever done. This demon- 
stration finally disposed of the aura seminalis which Harvey had 
found himself obliged to adopt on the grounds of his dissections on 
does. Curiously enough Spallanzani never convinced himself that 
the spermatozoa themselves were the active agents. 

3-13. Preformation and Epigenesis 

Of all the preformationists Charles Bonnet was the most theoretical. 
He was an adherent of that way of thinking mainly on the theoretical 
ground that the organs of the body were linked together in so intimate 
a manner that it was not possible to suppose there could ever be a 
moment when one or two of them were absent from the ranks. "One 
needs", he said, "no Morgagni, no Haller, no Albinus to see that 
all the constituent parts of the body are so directly, so variously, so 
manifoldly, intertwined as regards their functions, that their relation- 
ship is so tight and so indivisible, that they must have originated all 
together at one and the same time. The artery implies the vein, 
their operation implies the nerves which in their turn imply the 
brain and that by consequence the heart, and every single condition 
a whole row of other conditions." Bonnet compared epigenesis to 
crystal-growth in which particles are added to the original mass 
independently of the plan or scheme of the whole, i.e. in opposition 
to the growth of an organism, in which particles are added on only 
at certain places and certain times under the guidance of "forces de 
rapport". Przibram has recently discussed the question of how far 
such a comparison is admissible, but, in Bonnet's time at any rate, 
it became very famous. Bonnet made reference to Haller's discovery 
of the intimate relationship between embryo and yolk as evidence 


for his theory. The embryo begins, according to him, as an exceedingly 
fine net on the surface of the yolk, fertilisation makes part of it beat 
and this becomes the heart, which, sending blood into all the vessels, 
expands the net. The net or web catches the food particles in its 
pores, and Bonnet supposed that, if it were possible to abstract all 
the food particles at one operation from the adult animal, it would 
shrivel and shrink up into the original invisible web from which it 

Bonnet was no more afraid of the emboitement principle than was 
Haller; indeed, he called it "one of the greatest triumphs of rational 
over sensual conviction". Many of his arguments were reproductions 
of Haller's, and he says in his preface that he had written his book 
some time before Haller's papers on the chick appeared, but then, 
finding his own views confirmed by the more experimentally founded 
ones of Haller, he determined to publish what he had set down. Thus 
in one place he says, " I shall be told, no doubt, that the observations 
on the development of the chick in the tgg and the doe in the maternal 
uterus make it appear that the parts of an organised body are formed 
one after another. In the chick for instance it has been observed that 
during the early part of incubation the heart seems to be outside 
the animal and has a very diflferent form to what it will have. But 
the feebleness of this objection is easy to apprehend. Some people 
wish to judge of the time when the parts of an organised body 
begin to exist by the time when they become visible to us. They 
do not reflect that minuteness and transparency alone can make 
these parts invisible to us although they really exist all the 

Bonnet was therefore what might be called an " organicistic pre- 
formationist", for his objection to epigenesis lay in the fact that it 
apparently did not allow for the integration of the organism as a 
whole. His mistake was that he assumed the capacities of the adult 
organism to be present all through foetal life, whereas the truth is 
that they grow and differentiate in exactly the same way as the 
physical structure itself does. Bonnet's philosophical position, which 
has been analysed by Whitman, seriously contradicts the generalisa- 
tion of Driesch that all the epigenesists were vitalists and all the pre- 
formationists mechanists. For Bonnet an epigenetic and a mechanical 
theory were one and the same; he hardly distinguished, as Radl 
says, between Descartes and Harvey; and it was just the neo-vitalistic 


idea of the organism as a whole that he could not fit in with epigenesis. 
Needham and Wolff were undoubtedly epigenesist-vitalists, and 
Bonnet was undoubtedly a preformationist-vitalist, but Maupertuis 
was equally clearly an epigenesist-mechanist. 

G. L. Leclerc, Comte de Buffon, the most independent figure in 
the controversy, stood alone as much because of his erroneous experi- 
ments as because of his originality of mind. As has so often been 
observed, Buffon was not really an experimentalist at all: he was a 
writer, and preferred other people to do his experiments for him. 
The volume on generation in his Histoire Naturelle begins with a very 
long historical account of the work that had been done in the previous 
centuries on embryology. At the beginning of the section on repro- 
duction in general he said, "The first and most simple manner of 
reproduction is to assemble in one body an infinite number of similar 
organic bodies and to compose the substance in such a manner that 
every part shall contain a germ or embryo of the same species and 
which might become a whole of the same kind with that of which 
it constitutes a part". Such an idea resembles the ancient atomistic 
speculations, and is explicated by W. Smellie, the obstetrician, who 
translated Buffon into English, as follows: "The intelligent reader 
will perceive that this sentence, though not very obvious, contains 
the principle upon which the whole theory of generation adopted 
by the author is founded. It means no more than that the bodies 
of animals and of vegetables are composed of an infinite number 
of organic particles, perfectly similar, both in figure and substance, 
to the whole animal or plant of which they are the constituent parts ". 
This conception explains Buffon's curious attitude to the preformation 
question. An embryo was preformed in its germ because all the parts 
of the germ were each a model of the animal as a whole, but it was 
also formed by epigenesis because, the sexual organs being first 
formed, all the rest arose entirely by a succession of new origins. 
Buffon's "organic, living, particles" bear some resemblance to the 
"biogen molecules" which later generations were to discuss, and he 
says that an exactly similar but simpler structure is present in dead 

In his discussion of former theories he resolutely rejects the em- 
boitement aspect of preformationism, giving various calculations to 
show its impossibility and maintaining that "every hypothesis which 
admits an infinite progression ought to be rejected not only as false 


but as destitute of every vestige of probability. As both the vermicular 
and ovular systems suppose such a progression, they should be ex- 
cluded for ever from philosophy". He completely destroys the theory 
which the ovists and animalculists had set up in order to explain 
resemblance to parents, namely, that, although the foetus might 
originate either from egg or spermatic animalcule originally, it was 
moulded into the form of its parents by the influence of the maternal 
organism during pregnancy. This field, which was more than once 
disturbed by the contestants during the course of the century, re- 
ceived systematic attention from time to time by medical writers. 
There was a memorable dispute on this point between Turner and 
Blondel, whose polemics, written in an exceedingly witty manner, 
are still very pleasant and amusing to read. Blondel was the sceptic 
and Turner the defender of the numerous extraordinary stories which 
passed for evidence on this subject. It is interesting to note that 
Turner believed in the continuity of foetal and maternal blood-vessels. 
Krause and Ens later supported the opinions of Turner, while Okes, 
in a Cambridge disputation, argued against them. 

Buflfon's sixth chapter, in which he relates the progress of his own 
experiments, is unfortunate, in that his main result was to discover 
spermatozoa in the liquor folliculi of ovaries of female animals. The 
explanation of how he came to make such an enormous mistake 
has never been satisfactorily given, and it was not long before the 
truth of the observation was questioned by Ledermuller. It led him 
naturally to the assertion that the ovaries of mammalia were not egg- 
producing organs but animalcule-producing organs, and to the view 
that the beginning of embryonic development lay in the fusion of the 
male with the female spermatic animalcules — a curious revival of 
Epicureanism. But it is to be observed that he does not mean one 
male animalcule with one female animalcule, but rather all with all, 
in a kind of pangenesis. "All the organic particles", he says, "which 
were detached from the head of the animal will arrange themselves 
in a similar order in the head of the foetus. Those which proceeded 
from the backbone will dispose themselves in an order corresponding 
to the structure and position of the vertebrae". And so on for all 
the organs. The fact that for the organs common to both sexes a 
double set of animalcules will thus be provided does not give Buffon 
any difficulty and is fully admitted by him. Accordingly he could 
only agree to the aphorism omne vivum ex ovo in the sense of 


Harvey, namely, as referring to the egg-shaped chorion of vivipara, 
and definitely not in the sense of de Graaf and Stensen, namely, in 
the modern sense. "Eggs", he says, "instead of being common to 
all females, are only instruments employed by Nature for supplying 
the place of uteri in those animals which are deprived of this organ. 
Instead of being active and essential to the first impregnation, eggs 
are only passive and accidental parts, destined for the nourishment 
of the foetus already formed in a particular part of this matrix 
by the mixture of the male and female semen." Biology at this period 
was still labouring under the disadvantage of being without the cell- 
theory, and therefore unable to distinguish between an egg and an 

In spite of his leanings towards epigenesis, Buffon repeats precisely 
the error of Malpighi. "I formerly detected", he says, "the errors 
of those who maintained that the heart or the blood was first 
formed. The whole is formed at the same time. We learn from actual 
observation that the chicken exists in the egg before incubation. The 
head, the backbone, and even the appendages which form the 
placenta are all distinguishable. I have opened a great number of 
eggs both before and after incubation and I am convinced from the 
evidence of my own eyes that the whole chicken exists in the middle 
of the cicatrice the moment the egg issues from the body of the hen. 
The heat communicated to it by incubation expands the parts only. 
But we have never been able to determine with certainty what parts 
of the foetus are first fixed, at the moment of its formation." The 
experiment of taking a look at the cicatrices of eggs on their way 
down the parental oviduct is so obvious that Buffon must have thought 
of it, and it would be really interesting to know what factor in the 
intellectual climate it was that made him regard such an observation 
as not worth attempting. His observations on the embryo itself were 
good and, in some ways, new; thus he noticed that the blood first 
appears on the "placenta" or blastoderm, and for the first few days 
seems hardly to enter the body of the embryo. He gave an extremely 
good account of the whole developmental process in the chick and 
in man, and his opinions on the use of the amniotic liquid and the 
functions of the umbilical cord were very advanced. 

J. T. Needham, however, spoke very clearly in favour of epi- 
genesis, though he himself did no embryological experiments. His 
Idee sommaire of 1776, written against Voltaire, who had called him 

N E I 14 


a Jesuit and who had drawn materialistic inferences from his writings, 
contained the following passage: "The numerous absurdities which 
exist in the opinion ofpre-existent germs together with the impossibility 
of explaining on that ground the birth of monsters and hybrids, made 
me embrace the ancient system of epigenesis, which is that of Aristotle, 
Hippocrates, and all the ancient philosophers, as well as of Bacon 
and a great number of savants among the neoteriques. My observa- 
tions also led me directly to the same result". Needham's embryology 
is mostly contained in his Observations nouvelles sur la Generation of 
1750. He was explicitly a Leibnitzian and postulated a vegetative 
force in every monad. 

Needham was not the only thoroughgoing epigenesist of this 
period. Maupertuis, whose Venus Physique was published anony- 
mously in 1746, came out very clearly on the side of epigenesis. 
"I know too well", he said, "the faults of all the systems which I 
have been describing, to adopt any one of them, and I find too 
much obscurity in the whole matter to wish to form one of my own. 
I have but a few vague thoughts which I propose rather as thoughts 
to be examined than as opinions to be received, and I shall neither 
be surprised nor think myself aggrieved if they are rejected. It seems 
to me that both the system of eggs and that of spermatic animal- 
cules are incompatible with the manner in which Harvey actually 
saw the embryo to be formed. And one or the other of these systems 
seems to me still more surely destroyed by the resemblance of the 
child, now to the father and now to the mother, and by hybrid 
animals which are born from two different species. ... In this ob- 
scurity in which we find ourselves on the manner in which the foetus 
is formed from the mixture of two liquors, we find certain facts which 
are perhaps a better analogy than what happens in the brain. When 
one mixes silver and spirits of nitre with mercury and water, the 
particles of these substances come together themselves to form a 
vegetation so like a tree that it has been impossible to refuse it the 
name." This was the Arbor Dianae, which played a great part in 
these embryological controversies of the eighteenth century. It has 
a great interest for us, for it was perhaps the first occasion on which 
a non-living phenomenon had been appealed to as an illustration 
of what went on in the living body. It is true that Descartes long 
before had said that the movements of the living body were carried 
out by mechanisms like clocks or watches, and that they resembled 


the statues in certain gardens which could be made to perform un- 
expected functions by the pressure of a manipulator's foot on a 
pedal, but these instances were all artificially constructed mechanical 
devices, whereas the Arbor Dianae was a natural phenomenon quite 
unexplained by the chemists of the time, and the lineal forerunner 
of Lillie's artificial nerve, and Rhumbler's drop of chloroform. We 
know now that its formation is a simpler process than anything 
which occurs in the developing embryo, but the course of research has 
made it undeniably clear that the same forces which operate in the 
formation of the Arbor Dianae are at work also in the developing 
embryo. To this extent Maupertuis is abundantly justified, and 
Driesch's comments on him are not in agreement with the facts. 

"Doubtless many other productions of a like kind will be found", 
Maupertuis goes on, "if they are looked for or perhaps if they are 
looked for less. And although they seem to be less organised than 
the body of most animals, may they not depend on the same mechanics 
and on similar laws? Will the ordinary laws of motion suffice, or 
must we have recourse to new forces? These forces, incomprehensible 
as they are, appear to have penetrated even into the Academy of 
Sciences at Paris, that institution where so many opinions are weighed 
and so few admitted." Maupertuis goes on to speak of the contem- 
porary deliberations on the subject of attraction. "Ghymistry", he 
says, "has felt the necessity of adopting this conception and attractive 
force is nowadays admitted by the most famous chymists who have 
carried the use of it far beyond the point which the astronomers 
had reached. If this force exists in nature, why should it not take 
part in the formation of animals?" Maupertuis was thus an epi- 
genesist and a mechanist at the same time. His opinions have an 
extremely modern ring, and his only retrograde step was in suggesting 
that the spermatic animals had nothing else to do except to mix the 
two seeds by swimming about in them. But that legacy of ovism 
was common all through the eighteenth century, and thirty years 
later Alexander Hamilton could say, "From the discovery of Animal- 
cula in semine masculino by Leeuwenhock's Glasses, a new Theory was 
adopted which is not yet entirely exploded". 

But the real middle point and fulcrum of the whole period lay in 
the controversy between von Haller and Caspar Friedrich Wolflf, the 
former at Gottingen and the latter at St Petersburg in the Academy 
of the Empress Catherine. Kirchhoflf has described this polemic. 



Wolff's Theoria generationis, which was a defence of epigenesis on 
theoretical and philosophical grounds, written in a very formal, 
logical, and unreadable manner, appeared when he was only twenty- 
six years old, in 1759. Leibnitz, as Radl points out, had borrowed 
from the earlier preformationists the conception of a unit increasing 
in bulk in order to become another kind of unit; but Wolff, following 
Needham, borrowed from Leibnitz the idea of a monad developing 
into an organism by means of its own inherent force, and to this he 
joined the Stahlian notion of a generative supra-physical force in 
nature. On the practical side, Wolff's work was indeed of the highest 
importance. If the embryo pre-exists, he argued, if all the organs 
are actually present at the very earliest stages and only invisible to 
us even with the highest powers of our microscopes, then we ought 
to see them fully formed, as soon as we see them at all. In other 
words, at the moment at which any given organ comes into view, it 
ought to have the form and shape, though not the size, of the same 
organ when fully completed in the embryo at birth. On the other 
hand, if this is not the way in which development goes on, then one 
ought to be able to see with the microscope one shape changing into 
another shape, and, in fact, a series of appearances, each one different 
from that which had immediately preceded it, or, in other words, 
a series of advancing adaptations of the various parts of the primitive 
embryonic mass. WoliT chose as his first test case the blood-vessels 
of the blastoderm in the chick, for he saw that at one moment this 
apparatus was in existence, while the moment before it had not been. 
His microscopical researches led him to the conclusion that the homo- 
geneous surface of the blastoderm partially liquefies and transforms 
itself at these points into a mass of islands of solid matter, separated by 
empty spaces filled with a colourless liquid but afterwards with a red 
liquid, the blood. Finally, these spaces are covered with membranes 
and become vessels. Consequently it was obvious that the vessels had 
not been previously formed, but had arisen by epigenesis. 

Haller replied to this new experimental foundation for epigenesis 
without delay, for he was working on the development of the chick 
at the same time, and held closely to the opposite theory. We have 
already seen what his one and only argument against Wolff was. He 
used it time after time in all its possible variations, maintaining stoutly 
that the chick embryo was so fluid in the early stages that Wolff had 
no right to deny the presence of a given structure simply because 


he could not see it. Haller's explanation of Wolff's results was that 
the blood-vessels had been there all the time but that they had not 
become visible until the moment at which Wolff saw the islands 
forming. "After I had written the above", said Haller, "M. Wolff 
made new objections against the demonstration. Instructed by new 
researches, he denies absolutely that the yolk-membranes, which he 
makes two in number, exist before incubation. He pretends that they 
are new and that they are born at the beginning of incubation, and 
consequently that the continuity of their vessels with the embryo 
does not in the least prove that in the body of the mother the yolk 
received vessels from the foetus. I have compared the observations 
of this great man with my own and I have found that the yolk 
never has more than one pulpy and soft membrane, part of which 
is what I have called the umbilical area, and that the fine exterior 
membrane does not belong to the yolk but to the inner part of the 
umbilical membrane. ... I do not believe that any new vessels arise 
at all, but that the blood which enters them makes them more 
obvious because of the colour which it gives them, and so by the 
augmentation of their volume, they become longer." 

Wolff replied by another extensive piece of work, which he called 
De Formatione Intestinorum, and which appeared in one of the publica- 
tions of the Russian Academy for 1768. It ruined preformationism. 
In it he demonstrated that the intestine is formed in the chick by 
the folding back of a sheet of tissue which is detached from the ventral 
surface of the embryo, and that the folds produce a gutter which in 
course of time transforms itself into a closed tube. The intestine, 
therefore, could not possibly be said to be preformed, and from this as 
starting-point, Wolff went on to propose an epigenetic theory which 
applied the same process to all organs. It is interesting to note that 
the facts brought forward by Wolff have never been contradicted, but 
have been used as a foundation to which numberless morphological 
embryologists have added facts discovered by themselves. It is 
noteworthy that, although Wolff's second general principle, that of 
increasing solidification during embryonic development, led to no 
immediate results, it has been abundantiy confirmed since then (see 
Fig. 221). His observations on the derivation of the parts of the early 
embryo from "leaf-like" layers were even more important, and acteA 
as a very potent influence in the work of Pander and von Baer. 

It happened, however, that Haller had much the greater in- 


fluence in the biological world at the time, so that Wolff's conceptions 
did not immediately yield fruit in any general advance. Looking 
back over the second half of the seventeenth and the first two-thirds 
of the eighteenth century, it is remarkable how little theoretical 
progress was made in view of the abundance of new facts which were 
discovered. Punnett, in an interesting paper, has vividly brought this 
out. "The controversy between the Ovists and Animalculists had 
lasted just a century", he says, "and it is not uninteresting to reflect 
that the general attitude of science towards the problem of generation 
was in 1775 niuch what it had been in 1675. When the period opened, 
almost all students of biology and medicine were Preformationists 
and Ovists; at its close they were for the most part Ovists and Pre- 
formationists." Ovism sprang in the first instance from de Graaf's 
discovery of the mammalian egg, which gave a new and precise 
meaning to Harvey's aphorism. Preformationism, already old as a 
theory, acquired an apparent factual basis in the work of Malpighi 
and Swammerdam, and allied itself naturally with ovism. With 
Leeuwenhoek and his spermatozoa, animalculism came upon the 
field. The main outlines of the battle which went on between the 
two viewpoints have already been drawn, but it is worth remembering 
that there were independent minds who were impressed by the obvious 
facts of heredity and found it difficult to call one sex essential rather 
than the other. Among these Needham and Maupertuis might be 
counted, and among the lesser men, James Handley with his Me- 
chanical Essays on the Animal Oeconomy of 1730 ought to receive a 
mention. Though fond of theological arguments he upheld the 
common-sense attitude against ovists and animalculists alike — "We 
dissent in some things", he said, "both from Leeuwenhoeck and 
Harvey. . . . Both the semen and ova (notwithstanding all that can 
be said) we believe to be a causa sine qua non in every Generation". 
But what finally killed animalculism was the discovery in so many 
places of small motile living beings, flagellates, protozoa, large 
vibrios. It was difficult to maintain in the face of this new evidence 
that the spermatozoa were essential elements in generation, though 
the seminal fluid itself might very well be, as of course was Spallan- 
zani's opinion. The preformation theory was what was holding up 
further progress, and when Wolff's arguments prevailed in the very 
last years of the eighteenth century, the way was open for the 
recognition of the true value of the spermatozoa. 


The otherwise unknown physician d'Aumont, who wrote the 
article on "Generation" in Diderot's famous Encyclopaedia, brought 
this out in an interesting way, for himself an ovist, he summarised 
the arguments, which, in 1757, were destroying the animalculist 
position, and reducing rapidly the number of its adherents. 

1. Nature would never be so prolific as to produce such millions 
of spermatic animalcules, each one with its soul, unnecessarily. 

2. The spermatic animalcules of all animals are the same size, no 
matter how large the animal is: how, therefore, can they be 
involved in its generation? 

3. They are never found in the uterus after coitus, but only in 
the sperm (?). 

4. How do they reproduce their kind? 

5. What evidence is there that they are any different from the 
animalcules (of similar shape, etc.) which are to be found in 
hay infusion, scrapings from the teeth, etc. ? Nobody supposes 
that these have any relation to reproduction. 

3-14. The Close of the Eighteenth Century 

The last forty years of the century were not marked by any great 
movement in a fruitful direction for morphological embryology, an 
iconographic wave of some merit due to Albinus, W. Hunter, Tarin, 
Senffj Rosenmuller, Danz and Soemmering excepted ; and it was not 
until 181 2 that J. F. Meckel the younger translated Wolff's papers 
into German. This was one of the principal influences upon Pander 
and von Baer. In his introduction, Meckel describes how Wolff's 
work had been disregarded, and points out that Oken, writing in 
1806, had apparently never even heard of it. In the very early 
years of the nineteenth century morphological embryology received 
a great impetus, however. One of the most interesting figures of 
the new period was de Lezerec, a Breton, whose father had been 
in the Russian naval service. The son, as a Russian naval cadet, no 
doubt stimulated by the writings of Wolff, who had lived at St Peters- 
burg, used to incubate eggs on board ship. He eventually left the 
sea, studied medicine at Jena, and wrote an excellent dissertation 
on the embryology of the chick in 1 808, which Stieda has recently 
brought to light. He then went to Paris, and, taking a medical 
appointment at Guadeloupe, was lost to science. Very much more 
important was the work of Pander in 181 7 and von Baer in 1828, 


but it belongs to the present period, and I shall not treat it historically. 
For data on von Baer, see Kirste, Addison and Stieda. It is interesting 
to note, however, that the recapitulation theory, which was first clearly 
formulated by von Baer, was already taking shape in various minds 
during the closing years of the eighteenth century. Lewes has thus 
described the thesis of Goethe's Morphologie, written in 1795: "The 
more imperfect a being is the more do its individual parts resemble 
each other and the more do these parts resemble the whole. The more 
perfect a being is the more dissimilar are its parts. In the former case 
the parts are more or less a repetition of the whole, in the latter 
case they are totally unlike the whole. The more the parts resemble 
each other the less subordination is there of one to the other : and 
subordination is the mark of high grade of organisation". 

William and John Hunter belong also to the end of the century. 
The former, in his book on the anatomy of the gravid uterus, proved 
finally and completely the truth of the view that the maternal and 
foetal circulations are distinct. His injections left no shadow of doubt 
about the matter, and the way was clearly opened up for the study 
of the properties of the capillary endothelial membranes separating 
the bloods, a study which is still vigorously proceeding, especially 
in its physico-chemical aspect (see Section 21). There was a quarrel 
between the brothers over the priority of this demonstration. John 
Hunter's Essays and Observations also contain material important for 
embryology. His drawings of the chick in the &gg were very beautiful, 
and are still in the archives of the Royal College of Surgeons. He 
adopted Mayow's theory of the office of the air-space, and anticipated 
von Baer's theory of recapitulation much as did Goethe. "If we were 
capable of following the progress of increase of the number of parts 
of the most perfect animal as they were first formed in succession, 
from the very first to its state of full perfection, we should probably 
be able to compare it with some one of the incomplete animals 
themselves, of every order of animals in the creation, being at no 
stage different from some of the inferior orders. Or, in other words, 
if we were to take a series of animals, from the more imperfect to 
the perfect, we should probably find an imperfect animal corre- 
sponding with some stage of the most perfect." It is impossible not 
to reflect on the curious course which was taken by the essence of 
the idea of recapitulation in the history of embryology. As Aristotle 
first formulated it, it was as much bodily as mental, but all his sue- 


cessors until the eighteenth century a.d. treated it as a psychological 
rather than a physiological or morphological theory, and lost them- 
selves in speculations about the vegetative, sensitive, and rational 
souls. Yet the other aspect of the theory was only asleep, and was 
destined to be of the greatest value as soon as investigators began to 
direct their attention more to the material than to the spiritual 
aspect of the developing being. 

Hunter did not absolutely reject preformationism, but regarded it 
as holding good for some species in the animal kingdom ; he therefore 
attached no philosophical importance to it. 

Although Wolff's work did not lead to the immediate morphological 
advances which might have been expected, it was in many ways 
fruitful. It produced J. F. Blumenbach's Uber den Bildungstrieb of 
1789, a work which elaborated the Wolffian vis essentialis into 
the nisus formativus, a directing morphogenetic force peculiar to 
living bodies. It is interesting to note that Blumenbach passed through 
an exactly opposite succession of opinions to that of Haller, i.e. he 
was first attracted by preformationism, but, being convinced by 
Wolff's work, abandoned it in favour of epigenesis. Blumenbach 
compares his nisus formativus with the force of gravity, regarding 
them as exactly similar conceptions and using them simply as 
definitions of a force whose constant effects are recognised in 
everyday experience. Blumenbach says that his nisus formativus 
differs from Wolff's vis essentialis because it actively does the shaping 
and does not merely add suitable material from time to time to a 
heap of material which is already engaged in shaping itself. Wolff 
was still alive at this time, but he did not make any comment on 
Blumenbach, though he might very well have said that Blumenbach 
had misunderstood him, and that their forces were really alike in 
every particular. Both Blumenbach and Wolff were mentioned by 
Kant in the Critique of Judgement where he adopted the epigenetic 
theory in his discussion of embryogeny. 

A word must be said at this point about the opinions of the 
eighteenth century on foetal nutrition. At the beginning of it, there 
was, as has been shown, a welter of conflicting theories; and though, 
later on, writers on this subject were fewer, the progress made was 
no more rapid. In 1802 Lobstein was supporting the view (which 
had been defended by Boerhaave) that the amniotic liquid nourished 
the embryo per os, although Themel had shown forty years before 






that this could be at most the very slightest source of material, from 
a study of acephalic monsters. These workers had obviously learnt 
nothing from Herissant and Brady, who had been over precisely the 
same ground fifty years before. On the other hand. Goods and 
Osiander reported the birth of embryos without umbilical cords, so 
that the solution of this question became, in the first year of the 
nineteenth century, balanced, as it were, between the relative 
credibility of two kinds of prodigy. Nourishment per os was defended 
by Kessel, Hannes and Grambs, and was attacked by Vogel, Bern- 
hard, Glaser, Hannhard and Reichard. The idea lingered on right 
into the modern period, and as late as 1 886 von Ott, who was much 
puzzled about placental permeability, decided that a great part in 
foetal nutrition must be played by the amniotic liquid. WeidHch, 
a student of his, fed a calf on amniotic liquid for some days, and as 
it seemed to get on all right, he reported the amniotic liquid to have 
nutritive properties. The appeal to monsters was still resorted to at 
the end of the nineteenth century, for Opitz, in order to negative von 
Ott's conclusions, drew attention to a specimen in the Chemnitz 
Polyklinik in which the oesophagus of a well-nourished normal infant 
was closed at the upper third without the development of the body 
having been in any way restricted. The fuller possibilities of bio- 
chemistry itself have sometimes been exploited in favour of the ancient 
theory of nourishment />^r os\ thus Kottnitz in 1889 collected some 
data about the presence of peptones and protein in the human 
amniotic liquid with this object in view. That the foetus swallows 
the liquid which surrounds it towards the end of gestation in all 
amniota, can hardly be disputed, and as there are known to be 
active proteolytic enzymes in the intestinal tract, no doubt some of 
the protein which it contains is digested — but to maintain that any 
significant part is played in foetal nutrition by this process has 
become steadily more and more impossible since 1600. 

But to return to the eighteenth century; all was not repetition; 
occasionally somebody brought forward a few facts. Thus the de- 
glutition of the amniotic Hquid was discussed by Flemyng in 1 755 
in a paper under the title " Some observations proving that the foetus 
is in part nourished by the amniotic liquor". "I believe", he said, 
"that very few, if any at all, will maintain now-a-days with Claudius 
de la Courvee and Stalpartvan-der-Wiel, that the whole of its nourish- 
ment is conveyed by the mouth." But he himself had found white 


hairs in the meconium of a calf embryo with a white hide. Both 
Aides and Swammerdam had found the same thing, but Aides did 
not think it of any significance, and Swammerdam merely remarked 
that the calf must lick itself in utero. 

More interesting was W. Watson's "Some accounts of the foetus 
in utero being differently affected by the Small Pox". This was the 
earliest investigation of the permeability of the placenta to patho- 
logical agents. "That the foetus", said Watson, "does not always 
partake of the Infection from its Mother, or the Mother from the 
Foetus, is the subject of this paper." Two of his cases, he said, "evince 
that the Child before its Birth, though closely defended from the 
external Air, and enveloped by Fluids and Membranes of its own, is 
not secure from the variolous Infection, though its Mother has had 
the Distemper before. They demonstrate also the very great Subtility 
of the variolous Effluvia". But other cases "are the very reverse of 
the former, where though from Inoculation the most minute portion 
of Lint moisten'd with the variolous Matter and applied to the slightly 
wounded Skin, is generally sufficient to propagate this Distemper; 
yet here we see the whole Mass of the Mother's Blood, circulating 
during the Distemper through the Child, was not sufficient to pro- 
duce it. . . . From these Histories it appears that the Child before its 
Birth ought to be consider'd as a separate, distinct Organization; 
and that though wholly nourish'd by the Mother's Fluids, with 
regard to the Small Pox, it is liable to be affected in a very different 
Manner and at a very different Time from its Mother". Doubtless 
the modern explanation of Watson's discordant results would be that! 
in one case there were placental lesions, destroying the perfect barrier 
between the circulations, and in others there were not. 

In the last year of the century (but the seventh of the Republic) 
Citizens Leveille & Parmentier contributed an interesting paper to I 
the Journal de Physique in which they observed the increase in size] 
of the avian yolk on incubation and spoke of a current of water yolk- 
wards (see Fig. 225). 

3* 15. The Beginning of the Nineteenth Century 

At the beginning of the new century a fresh influence came in! 
with the work of Lamarck, though it did not have such a great effect 
on his contemporaries as on later generations. Its relations with] 
biochemistry are so remote that there is no need to deal in any detail 


with it here, but Lamarck's opinions on embryology may perhaps 
be given in the words of Cuvier, written in 1836. 

"In 1802 he pubUshed his researches on living bodies, containing 
a physiology peculiar to himself, in the same way that his researches 
on the principal facts of physics contained a chemistry of that char- 
acter. In his opinion the egg contains nothing prepared for life 
before being fecundated, and the embryo of the chick becomes 
susceptible of vital motion only by the action of the seminal vapour; 
but, if we admit that there exists in the universe a fluid analogous 
to this vapour, and capable of acting upon matter placed in favour- 
able circumstances, as in the case of the embryon, which it organises 
and fits for the enjoyment of life, we will then be able to form an 
idea of spontaneous generations. Heat alone is perhaps the agent 
employed by nature to produce these incipient organizations, or it 
may act in concert with electricity. M. de Lamarck did not believe 
that a bird, a horse, nor even an insect, could directly form them- 
selves in this manner; but, in regard to the most simple living 
bodies, such as occupy the extremity of the scale in the different 
kingdoms, he perceived no difficulty; for a monad or a polypus are, 
in his opinion, a thousand times more easily formed than the embryo 
of a chick. But how do beings of a more complicated structure, such 
as spontaneous generation could never produce, derive their existence? 
Nothing, according to him, is more easy to be conceived. If the 
orgasm, excited by this organizing fluid, be prolonged, it will aug- 
ment the consistency of the containing parts, and render them 
susceptible of reacting on the moving fluids which they contain, and 
an irritability will be produced, which will consequently be possessed 
of feeling. The first efforts of a being thus beginning to develope 
itself must tend to procure it the means of subsistence and to form 
for itself a nutritive organ. Hence the existence of an alimentary 
canal. Other wants and desires, produced by circumstances, will 
lead to other efforts, which will produce other organs : for, according 
to a hypothesis inseparable from the rest, it is not the organs, that is 
to say, the nature and form of the parts, which give rise to habits 
and faculties ; but it is the latter which in process of time give birth 
to the organs. It is the desire and the attempt to swim that produces 
membranes in the feet of aquatic birds; wading in the water, and 
at the same time the desire to avoid getting wet, has lengthened the 
legs of such as frequent the sides of rivers; and it is the desire of flying 


that has converted the arms of all birds into wings, and their hairs 
and scales into feathers. In advancing these illustrations, we have 
used the words of our author, that we may not be suspected either of 
adding to his sentiments or detracting any thing from them." 

If the latter part of the eighteenth century did not produce the 
move forward in the morphological direction which might have been 
expected from the work of Wolff, a remarkable amount of work was 
accomplished on the chemical side. This mass of work did not spring 
from any one source, it was not due to a great discovery on the part 
of one man, but rather it came about that, as the technique of 
chemistry itself improved, a number of otherwise undistinguished 
investigators, such as Dehne, Macquer and Bostock, applied physico- 
chemical methods to the embryo, though it is true that among the 
names are those of certain great chemists, such as Scheele and 
Fourcroy. The results of this movement were summarised in the work 
of J. F.John, whose Chemische Tabellen des Tierreichs appeared in 1814. 
With this date I propose to bring my historical assessment to an 
end. The work that was done in physico-chemical embryology 
after 181 4 will be considered in the appropriate sections dealing 
with the problems of the present time; for Gobley, as an example, 
who gave the name to the substance still called vitellin, was working 
only a dozen years after the date of the publication of John's 

In this translation of the Tables, I have made one alteration only. 
John groups together a number of data which are contained in von 
Haller's Elementa Physiologiae, and attributes them to that great man. 
But actually they were obtained by earlier investigators and only 
came to John through the medium of Haller and Fourcroy — I have 
therefore allotted them to their true originators. 


Substance or liquid 

investigated Composition 

Amniotic liquid (man) It contains a substance which can be 
precipitated with tincture of gall, 
phosphate of lime and muriatic salts 
„ It is salt 

„ It is sweet 

,, It coagulates on boiling 













Barbati & 



SECT. 3] 




Substance or liquid 

Amniotic liquid (man) 

Cheesy material, given 
off into the amniotic 
liquid by the body of the 
foetus (man) 

Embryonic tissue-juice 

Amniotic liquid (cow) 

Amniotic and allantoic 
liquids (cow) 


It is miscible with water 
It is coagulable by tincture of gall 
It is coagulable by alcohol 
It is coagulable by alumina 
It is coagulable by spirits of nitre 
Free mineral alkali, water, albumin- 
ous substance, common salt 
Much water, very little common 
salt, fire-stable alkali, phosphoric 
acid, some earth, and oxyde of 

Much water, a lymphatic coagulum, 
common salt, salmiac, a trace of 
phosphate of lime 
Sp. g. 1-005. Albuminous matter, 
soda, muriate of soda, phosphate of 
lime, the rest is water 

Animal slime, and a characteristic 
fatty material, or rather an albu- 
minous material tending to fat, car- 
bonate of lime 

It contains hydrofluoric acid 

Water, much sulphate of soda, 
phosphate of lime and talc, an 
animal substance soluble in water, 
insoluble in spirits of wine, and 
not forming a combination with 
tannic acid, a crystalline amniotic 

The liquid of the allantois is very 
different quantitatively in the dif- 
ferent periods of pregnancy, as also 
in the qualitative aspect of its com- 
position. First it is crystalline and 
colourless, then it gets yellowish, 
and finally a dark reddish-brown. 
But it remains watery all the time 
and never has the property possessed 
by the amniotic liquid, of becoming 
at last quite slimy even to the point 
of showing fibres in it. During the 
last months the hippomanes appear 
in it, these are soft and yet tough. 
The quantity of this liquid is much 
greater at the end than at the be- 
ginning. Alcohol precipitates from 
it a very large amount of a reddish 
substance; sulphate of baryta, tar- 
taric acid, and carbonate of lime 
give a large precipitate. These re- 
agents do not change the amniotic 
fluid at all. 1000 gm. Uq. allant. 
gave 20-25 gm. solid residue, 
1000 gm. liq. amnii gave lo-i i gm. 
solid residue 













Gmelin & 



van den Bosch 



Vauquelin & 

Vauquelin & 


Buniva & 







Substance or liquid 

Blood of embryo (man) 

Blood of embryo (rabbit) 

Foetal urine (man) 
Meconium (man) 

Meconium (cow) 

Eggs (wild birds) 





Composition Investigator 

Soda, much serum, and some leathery Fourcroy 

fibrous threads, which made up 

only ^ grain out of 3 gros 6 grains 

of cruor . They were jelly-like in con- 
sistency. No phosphoric acid. It 

differed from the blood of an adult 

(i) in not giving a red flush when 

shaken up with air, (2) in not clot- 
ting in air, (3) in the fibres being 

more jelly-like 
Does not coagulate in the cold but Fourcroy 

gives rise to a red serum tending 

towards brown. It was not as solid 

as usual except when heated, then 

it went grey though the supernatant 

liquor was red 
It is odourless and colourless and of Fourcroy 

a slimy nature 
Water f , ^r> spirituous extract similar Bay en 

to gall, a black residue dissolving 

partially in water to give a yellow 

colour. He holds it to be a milky 

Contains true gall-like substances 



Does not contain air of different com- 
position from atmospheric air 

Phosphate of lime, animal glue, and 
some combustible substance which 
escapes with a sulphurous smell 
from shells when they are softened 
in acid. Ferrous particles. Some- 
times some common salt. An egg, 
which weighed 2 ozs. 2 scruples 15 
grains, had white which weighed 
10 qentchen 2 scruples, yolk ^ oz. 
\ scruple, and shell and membranes 
2 drachms 5 grains 

An animal material insoluble in acids 

6 qentcfwn 2 scruples 7 grains lost 
practically 6 qentchen in drying, it 
contains no caustic salts, the ash is 
an earthy insipid dust 

Albuminous matter, water, muriate 
of soda, phosphate of lime, and 

Albuminous matter, oil, yellow pig- Adet 

From 60 eggs, 5^ ozs. oil Dehne 

Albuminous matter with much Adet 

Carbonate of lime, phosphate of lime, Adet 
and very oxydised albuminous 

Buniva & — 

Hehl 1 796 

von Wasserberg 1 780 

von Wasserberg 1 780 
von Wasserberg 1 780 


SECT. 3] 



Substance or liquid 


Eggs (domestic hen) 

Investigator Date 


A fine earth and a gelatinous material 
True lime, containing perhaps phos- 
phoric acid 
\ oz. of pulverised clean shell, di- 
gested with spirits of wine, gave i \ 
grains of an extract which smelt and 
tasted rancid. The same amount of 
shell gave i scruple of a yellow 
watery extract which tasted salt 
Carbonate and phosphate of lime, 
traces of a jelly, which can be used 
as gum. Phosphoric acid can be 
had from the ash 
Carbonate and phosphate of lime, 
bitter earth and iron, a jelly which 
can be used as gum 
Carbonate of Hme 72 parts, phos- 
phate of lime 2, jelly 3, water and 
loss 23 
Carbonate of lime 89-6 parts, phos- 
phate of lime 5-7, animal substance 
4-7, traces of sulphur. As a hen lays 
130 eggs in six months and as an 
egg weighs on an average 58-117 
grams, 7486-226 grams of solid must 
be used for egg-production in that 
time, i.e. since the shells would 
weigh 64-685 gm., 7333-793 gm., 
14 pounds 15 ounces 7 gros 8 
grains. The secretion of the lime is 
probably accomplished by means 
of the kidneys 
Carbonate and phosphate of lime, 
and jelly 
Very much carbonate of lime, very 
little phosphate. Traces of phos- 
phate of iron, earthy carbonates, 
rnuriates, albuminous and gela- 
tinous substance to hold it together. 
I cannot find any uric acid in it, as 
Vauquelin says is there, nor is he 
right in saying that the sulphur is 
in the shell — it is in the membranes 
only, and under the form of sul- 
phuric acid 

Consist of an animal material 
Have the properties of the fibrous 

part of blood 
A jelly-like material, soluble in hot 

An animal substance with traces of 

phosphate of lime, carbonate of 

lime, muriates, and a sulphurous 

An albuminous substance containing 

traces of sulphur and soluble in 

caustic potash 





1 781 



Merat-Gaillot — 

Vauquelin 1 799 








Vauquelin — 




Substance or liquid 





Egg (Snipe, Tringa vanellus) 


An agglutinative substance insoluble 
in water, apparently like dried tra- 
gacanth gum 

A white lymphatic transparent sticky 
slimy material 

Soda, albuminous matter, water, 

Water, albuminous matter, with 
some free alkali, phosphate of lime, 
muriate of soda, and sulphur 

Contains benzoic acid 

Water 80 parts, uncoagulable sub- 
stance 4-5 parts, albuminous matter 
15-5 parts, traces of soda, sul- 
phuretted hydrogen gas, and ben- 
zoic acid 

Contains sulphur 

Water, albuminous matter, a little 
jelly, soda, sulphate of soda, muriate 
of soda, phosphate of lime, oxyde 
of iron (?) 

An oxydised albuminous substance 
Apparently an albuminous substance 

Consists of a lymphatic material and 

a fatty oil 
Water, oil, albuminous matter, jelly 
Water, oil, albuminous matter, jelly, 
phosphates of lime and soda, with 
other salts 
Water, oil, albuminous matter 
Water, a mild oil, albuminous matter, 
a colouring matter which is perhaps 
Water, a yellow mild oil, traces of free 
(phosphoric?) acid, a small amount 
of a reddish-brown material, not 
fatty, and soluble in ether and warm 
alcohol, a jelly-like substance, a 
great deal of a modified albuminous 
substance, and sulphur 

Egg (lizard, Lacerta viridis) 


Egg (fish, salmon) 

Is composed of the same constituents 
as that of the hen, but the dark 
green pigment and the dark brown 
splashes are probably oxyde of iron 

A yellow oil, an albuminous material, 
and salts 

Diflfers from that of fowls in being 
granular and greasy when hardened 
by boiling 

420 grains contained of pure dry 
albuminous matter 26 grains, of a 
viscous oil 18 grains, insoluble al- 
buminous matter 102 grains, mu- 












Fourcroy — 

John — 

Macquer 1781 

Thomson — 

Hatchett — 

Jordan — 

Fourcroy — 








Substance or liquid 

investigated Composition Investigator Date 

riate of soda and sulphuric alkali 
28 grains, jelly, phosphate of lime, 
and oxyde of iron 2 grains, water 
242 grains 

Egg (fish, Cyprinus barbiis) Contains a substance dangerous for Crevelt — 

man, the nature of which is unknown 

Egg (insect, Locusta viridissima, and migratoris) 

Shell An animal combustible substance John — 

and phosphate of lime 

Contents Albuminous matter, a yellow fluid John — 

fatty oil, a little jelly and a charac- 
teristic substance, acid, phosphates, 
and sulphuric alkali 

The most interesting of the investigators in this table is Dzondi, 
whose work in 1806 was the first in which definite chemical charac- 
teristics were systematically followed throughout embryonic develop- 
ment. It is surprising that so long a time should have elapsed between 
Walter Needham and John Dzondi: no less than 139 years. 

After 1 8 14 events were to move so rapidly in the world of science 
that it would not be possible to follow all the embryological work 
that was done, and at the same time maintain the proper proportion 
between the historical part of this book and the other parts. The 
eighteenth century was the period during which the chemical side 
of embryology began to differentiate and split itself off from the rest. 
After 1 8 14 it pursued a course of its own, the individual tracks of 
which I shall mention under their appropriate heads. But another 
century had yet to pass before the value of the physico-chemical 
approach to embryology could become generally recognised, and we 
are ourselves only at the very beginning of this new period. 

A certain contrast may appear between the critical treatment 
which I have given to the investigators whose work I have been 
discussing, and the saying of William Harvey's — "all did well", 
which stands prefixed to this Part of the book. Yet history without 
criticism is a contradiction in terms, and the praise and dispraise, 
which I have tried to allot as accurately and justly as I could, is, 
as it were, technical, rather than spiritual. All the workers who have 
been mentioned, and others besides them who left no special marks 
on their time, are worthy of our respect and of our fullest praise, 
for they preferred wisdom before riches and, according to their 
several abilities and generations, diligently sought out truth. 



All things began in order, so shall they end, and 

so shall they begin again, according to the ordainer 

of order and the mystical mathematicks of the city 

of heaven. 

Sir Thomas Browne. 


There have already been certain reviews of work in chemical embryo- 
logy as a whole, among which those of Paechtner and Schulz are 
the most valuable. The former dealt almost exclusively with the 
chemistry of the egg from a static viewpoint, and only devoted a 
short section to the metabolism of the embryo during its develop- 
ment, while the latter, though dealing specifically with embryonic 
metabolism, gave hardly more space to it than Paechtner. In both 
cases the discussion was little more than a catalogue of references, 
and in neither case was the literature anything like complete, in- 
cluding, indeed, less than a tenth of the relevant citations. 

The first review of chemical embryology was written by Grafe in 
19 10, but, though he outlined several valuable ideas, it is now of 
small importance. Good information may, however, be found in 
Aron's monograph on the chemistry of growth and on the mammalian 
side there are Harding and Murlin. Other, less satisfactory, reviews 
are by Cazzaniga and Steudel. Finally there is, of course, an 
immense amount of work which can be found in no review, for 
investigators have followed the counsel of Godlevski (1910): "Un- 
sere Kenntnisse hinsichtlich der chemischen Zusammensetztung der 
Eier noch lange nicht ausreichend sind, so waren weitere Forschungen 
auf diesem Gebiete auch aus dem Grunde sehr erwunscht weil sie 
den Ausgangspunkt fiir die Physiologic des embryonalen Stoff- 
wechsels welcher bisher gleichfalls nur sehr wenig untersucht wurde, 
bilden mussen". 

Every effort has been made to give an accurate and complete 
presentation of the data in the Tables of this book and of the 
experimental conditions under which they were obtained, but 
investigators should always consult in addition, whenever possible, 
the relevant original memoirs referred to in the Bibliography. 



I -I. Introduction 

In giving an account of the present state of our knowledge about the 
chemical constitution of the egg-cell and the food-material which is 
accumulated around it or inside it, I shall not follow a strictly logical 
order of exposition, according to the phyla of systematic biology. 
I have judged it best to begin with the egg of the hen, for not only 
is it the most familiar and the best known of all eggs, but it is also 
the one which has been most thoroughly investigated biochemically. 

It should be remembered that the two main morphological divisions 
of the egg, (a) the egg-cell itself and {b) its coverings, appear in 
protean modifications throughout the animal kingdom. The former 
may be a simple cell with its ooplasm, nucleus, nucleolus, etc., as in 
the echinoderms, and no covering at all save its cell-membrane, or 
at the other extreme it may be swollen up with food-material or yolk 
to the prodigious proportions of the avian egg-cell. The membrane 
again may be a thin coat of investing cells such as the tunicate egg 
possesses, or it may be the jelly of the amphibian egg, or, again, it 
may be the complex arrangement of egg-white, chalazae, shell- 
membranes, and shell, which is present in the bird's egg. All imagin- 
able degrees of richness in yolk are present in the egg-cells of animals, 
and upon this fact depend the various kinds of cleavage which they 
show: alecithic eggs, on the one hand, such as those of most inverte- 
brates, having a holoblastic form of development in which the whole 
egg participates in cleavage; and yolk-rich eggs, on the other hand, 
such as those of most vertebrates, having a meroblastic development, 
only a localised part of the egg undergoing cleavage, the rest remaining 
as a sac full of yolk until it is finally absorbed. 

1-2. General Characteristics of the Avian Egg 

After the historical introduction which has been given, it should be 
unnecessary to remark on the general arrangement of the bird's egg. 
We have with Harvey referred to it as an exposed, and, as it were, 
detached uterus, and with Fabricius ab Aquapendente we have 


enumerated the parts of the typical avian ovum. Fig. 13, however, 
shows the general disposition of parts diagrammatically. 

First, as to size and shape. The size and shape of the egg were shown 
by Curtis in 191 1 and by Surface in 191 2 to be due partly to the 
structure of the oviduct, which very probably may be considered an 
inherited character, as was claimed by Newton. D'Arcy Thompson's 
discussion of the mechanics of egg-formation in birds, in his Growth 

" White or Milky Yolk 

\ Germinal Di^c .Pander's Nucleus 
Shell -Membranes ^ ^ ' t- _ , ^ 



Chalazae ^^^^^^'^ ' "^ ...^'^ ^ 

(Treadles, HailstOTie^r^^^::;^^^ I ^ ^^^^^^'^ ^, \ 

y, ^^=^^^^^ — 1-______-^ ^^^^'^ Chalazae 

/■ «r~ I ^; ^ 

Vitelline Membmne Haloes or ^ 

Layers of Yellow Yolk ^Whi te 

Fig. 13. Diagrammatic representation of the hen's egg. The chalazae were called by 
Tredern Ligamenta albuminis. Bartelmez gives a discussion of the factors governing 
the angle which the embryonic axis makes with the axis of the egg as a whole. The 
yolk is not a perfect sphere but lengthened along the main axis. The egg-white 
is divisible into three layers which increase in density from without inwards. The 
chalazae, as Berthold was the first to find, are not present in reptilian eggs. 

and Form, will be famiHar, but some biologists, such as Horwood, 
have taken exception to his conclusions about the physical influences 
which shape the egg. Ernst's well-known experiment was the starting- 
point of these discussions ; she caused hens to lay on a surface of wet 
sand and charcoal, and so, observing the process, found the blunt end 
to be blackened. This was in agreement with many other observers, 
such as V. Nathusius; Landois; Jasse; Konig-Warthausen and Erd- 
mann; and d'Arcy Thompson accordingly described the hen's egg 
as moving down the oviduct blunt end forwards, the pointed end 
owing its form to the peristaltic compression of the oviduct. Unfor- 


tunately all observers agree (Purkinje; von Baer; Coste; Kiitter; 
Taschenberg; Wickmann and Patterson for the hen, Blount and 
Patterson for the pigeon, Kiitter for the hawk, and Wickmann for 
the canary) that the pointed end passes first down the oviduct. It 
appears that the egg must turn right round in the act of being laid, 
and Bartelmez, indeed, has seen this occur. Curtis has shown that 
the shape of the egg depends to some extent upon its size and this 
biometric observation was afterwards confirmed by Pearl & Curtis. 
Many abnormalities have been reported in eggs. They need merely 
be mentioned here with their authorities, thus : 





Eggs containing masses of tissue^ more or less organised. 

von Nathusius. 



Dwarf eggs. 

Pearl & Curtis. 



Ovum in ovo. 






Pearl & Curtis. 



Roberts & Card. 


Double and triple-yolked eggs. 


Parker. ' 




Inadequate shell. 

Riddle & King. 

Dwarf or absent yolk (ovum centennium^). 


^ See Sir Thos. Browne, Pseudodoxia Epidemica, Bk iii, ch. 7, "Of the basilisk". The eggs 
of Chelonia also, according to Deraniyagala, are sometimes laid without yolks. 


It is interesting in this connection that Riddle has traced the 
occasional production of eggs with deficiency of white and shell but 
not of yolk, to a lack of the thymus hormone which he has called 
"Thymovidine". Feeding with desiccated thymus removed com- 
pletely these effects. "The whole of the data", he said, "seem to 
demonstrate the presence in the thymus of a substance having a highly 
specific action on the oviduct of birds — and presumably on that of all 
those vertebrate animals which secrete egg-envelopes." The syndrome 
involved eggs with normal yolks but hardly any shell or albumen, 
frequent reduction of normally paired ovulations to single ovulations, 
diminished fertility, and restricted hatchability of the eggs. "Though 
not necessary to the life of the individual", said Riddle, "thymo- 
vidine would seem to be essential to the perpetuation of those verte- 
brate species whose eggs are protected by egg-envelopes. Such 
animals were the ancestors of mammals and thus mammals could 
hardly have come into existence without the thymus." These con- 
siderations are of much interest in view of other speculations on the 
evolutionary aspect of chemical embryology, e.g. Section 6-6. They 
also suggest that the mammalian thymus is now a vestigial organ. 

The air-space, the shell and the white of the normal egg need no 
special remark at present, but the yolk is a more complicated structure. 
Around a central core of "white" or "milky" yolk the yellow yolk is 
secreted in the ovary of the hen in concentric layers, which form the 
appearance of "haloes" in the finished egg, and which show up es- 
pecially clearly when the hen is fed on Sudan III or some other non- 
toxic dye which has a selective staining action on fat. The white yolk 
in the centre is continued in a flask-like shape (the latebra) up to the 
surface of the yolk underneath the germinal disc, and is then con- 
tinued in a very thin layer all round the exterior of the yolk under- 
neath the vitelline membrane. The white yolk is thus the first 
nourishment of the embryo. It is not certain whether there are 
also layers of white yolk between the concentric layers of yellow yolk, 
for they have never been analysed chemically, and Balbiani main- 
tains that they only differ from the yellow layers by having less yellow 
pigment. The differences between the true white yolk and the yellow 
yolk are, as will be seen later, far more profound. Balfour & 
Foster, in their Elements of Embryology of 1877, described the yellow 
yolk as consisting histologically of spheres of from 25 to loo/x in 
diameter, filled with numerous minute highly refractive granules and 



[PT. Ill 

very susceptible to crushing and rough treatment. After boihng, the 
spheres assume a polyhedral form. The granules seen within them must 
consist of protein, for they are not soluble in ether or alcohol. On the 
other handjthe white yolk elements are vesicles smaller than the globules 
of the yellow yolk, being about 4 to 75 /n across, with a highly refractive 
body, often as small as i [x, in the interior of each. These vesicles are 
sometimes collected together into much larger vesicles. They observed 
also underneath the blastoderm or the germinal disc a number of 
large vacuoles filled with fluid — large enough, in fact, to be seen with 
the naked eye. The histology of yolk has been reviewed by Dubuisson, 
and at one time many papers were published on it, e.g. those of 
Virchow. They cannot be considered in detail here. 

1-3. The Proportion of Parts in the Avian Egg 

Of the weight of the whole egg, the shell takes up about 10 per 
cent., the albuminous white 50 per cent, and the yolk 30 per cent, 
in round numbers. These relationships have been determined by a 
multitude of investigators, whose results are drawn up in Table i . 

Table i . Distribution of the parts in the egg, 

Italic figures represent dry weight only. 


egg weights 










and date 

Hen, Polish i 





van Hamel-Roos ('.890) 

,, Polish ii 






,, Holland (Zwol.) 






„ Holland (Tiel) 











Miinster Ag. Sta. (1900) 






Drechsler (1896) 












Plimmer (1921) 



I i-i 








Langworthy (190 1-2) 
































Lebbin (1900) 





Welmanns (1903) 






Segin (1906) 






Liihrig (1904) 







Hen (various breeds) 





von Czadek (191 7) 





Rose (1850) 







Hen (various breeds) 





Carpiaux (1903) 






Lehmann (1850) 






Prout (1859) 






Poleck (1850) 



Stained by Kossa's method for the detection of calcium phosphate. The considerable 
variations in the vitelline globules may be noted. Magnification, 6xD: prepared and 
microphotographed by Dr V. Marza. 



SECT. l] 



Table i {cont.) 


egg weights 










and date 

Hen, Leghorn 





Murray (1925) 

Hen (various breeds) 





Iljin (1917) 












van Meurs (1923) 












Voit (1877) 

Nidicolous birds 






Tarchanovf (1884) 

Starling ... 


















Canary ... 






Thrush ... 





J J 


















Nidifugous birds 

























Turkey ... 























Glikin (1908) 






Davy (1863) 



























3 J 

Golden-crested wren 





) ) 




















J J 






J J 





















Hartung (1902) 





Voit (1881) 



Fere (1896) 











Pott & Preyer (1882) 






Rozanov (1926) 






Hepburn & Katz (1927) 











Baudrimont & de 
St Ange (1846) 

Dwarf hen ... 





Sacc (1847) 




Pott (1879) 





Atwater & Bryant ( 1 906) 


■f- All Tarchanov's figures exclude the shell weight. 



[PT. Ill 

Table i 


Weight of 








tents (gm.) 





and date 


• 57-12 





Friese (1923) 


• 137-38 






781 1 






• 92-93 


















• 25-40 












. 27-03 





Blackbird ... 
















Weight of 








ents (gm.) 




and date 

Plover ( Vanellus crist 






Bauer (1893-5) 

Hen {Gallus domestict 







Guinea-fowl {Meleag 

ris gallopavo) 





Swallow (Hirundo ru. 






Partridge [Perdrix ci 






Sparrow {Passer dom 






Thrush (Turdus 

? ) ... 





Duck (Anas) [doubl 






The above data were all obtained without any ad hoc investigation of the probable 
errors involved in weighing eggs and parts of eggs. An elaborate study by M. R. Curtis 
in 1 9 1 1 gave the following results on Gallus domesticus : 

weight in gm. % 

56-04 100 

33-22 59-26 

16-31 29-14 

6-28 ii-i8 

0-23 0-42 

Whole egg 


Shell and membranes 

But though this is the case with the egg in its natural state, the solid 
matter is concentrated much more in the -yolk than in the white, 
so that, as the analyses of Poleck and Iljin, for instance, show, for 
dry weight the conditions are exactly reversed. The egg-white may, 
indeed, be regarded as the principal reservoir of water for the embryo 
which develops on dry land, and this is a point which will be dis- 
cussed later (see Section 6-6). The eggs of different breeds of hen 
vary to some extent in the relative weights of shell, white and yolk; 
but, although it is difficult to lay down any general rule, these varia- 
tions do not greatly exceed the variations due to factors connected with 
the individual hen. Iljin's lightest shells make up about 7 per cent, 
of the G,gg weight and the heaviest not more than 11-5 per cent. 


It is certain that there are constant differences between the eggs of 
different breeds, but as a whole these are quite outweighed by 
individual differences, and only appear when extended statistical 
studies are undertaken. The eggs of other birds, however, do not fall 
within these limits. Langworthy, for example, has shown that, in 
the duck's egg, the shell may account for as much as 14 per cent, 
of the whole weight. A similar result was found for the turkey and 
the goose, while the guinea-fowl's egg has a shell of nearly 1 7 per 
cent, of the whole weight. The wide series of Friese, shown in Table i, 
seems to indicate that the larger the egg the more shell it has to 
have : thus the canary's egg weighing just under 2 gm. has 4 per cent, 
while the goose's egg which weighs 137 gm. has 14 per cent. Heinroth, 
and Groebbels & Mobert, among others, have collected a great 
many data of this kind for all varieties of bird, but their papers must 
be referred to for the figures. Thus the fertilised embryo starts its 
development on the surface of a mass of food only slightly diluted 
with water, and surrounded by a further and much wetter supply. 
This is reflected well by the work of Bellini, who found that the yolk 
of the hen's egg was seven times as viscous as the white at the begin- 
ning of development. (Alb. 3-4 units, yolk 28-5 units.) 

A good deal of work has been done on the variability of the 
weights of the parts of the egg within a given species of fowl. Thus 
Jull found that egg weight is the least variable factor, albumen 
weight slightly more variable than egg weight, yolk weight con- 
siderably more variable than albumen weight, and shell weight the 
most variable. It would seem, therefore, as if a compensatory process 
takes place during egg-production, the largest yolks having the 
smallest whites, since the weights of the entire eggs do not vary as 
much as the weights of the components. On the other hand, the 
smaller eggs contain the highest percentage of albumen and shell 
and the lowest percentage of yolk. Jull also studied closely the 
seasonal variations, which may be quite considerable, finding that 
the component parts of the egg contribute in different degrees at 
different times of the year towards the total egg weight. The question 
as to which part of the egg is mainly responsible for large or small 
eggs is still debated, for Curtis concluded from his observations that 
it is the egg-white, while Atwood found many indications contrary 
to this. Statistical studies on the egg of the tern have been made by 
Rowan, Parker & Bell; Rowan, Wolff, Sulman, Pearson, Isaacs, 



[PT. Ill 

o V 

CO „ 


« CO 

c -n CO -C CO-X3 
•s ^eo 3 CO Kj 

(V^ 3 . .c?i ^ C 1- 


"£ ^q o ^^C5 g o 3 

CL, ^ U CM ^ < O pa 

S ^ 



o 05 y <^ 


:: -s 



O «3 Thin 9 r^ 

.t! to CO CO r^ <i 

^ I 















a i 

o « 

.§ 3 -a 

'S o o 

i c f3 

C « i- 

o botJ 

[i, O CO " O CO 

to « CO Crs N 1^ 

« cn 05 o Oi^ ts o Co o O) 0500 oico o 05 oj 9 cp 

<o lO c<-)Co e« lOif^Tj^crjc* fso o> r^<o cn 7^ ^p 

• 3 co^ri " CO CT> 

V m CO t^t^ ■* 

O !£> « CO CO " 

&3 " " " " " 

f~- Tf< OiQS O^COkiCO 0^';*'C\| LOOjf^ t-v<0 ^ CO 


CO to o oi 

■;*" r^ iT)^ CO lOCp ^ ts ^ irjCO irj '^ d-j s 7^ f^ 
N e» coTfcoei " I -^,'^ 6 ,0 CD 6^ eo.crj m ,0 ■^,f^.,ir) n ■^ 



••::•:::::::::•:::: : : : : : "^ 
« ;i:;rr.; iiii^tiii* 

u o -H c 

c oc>c.„.u.o„i2-.S >"a.c7^ 

ffi qjuohK q o h o (!< s hi 

SECT. l] 





'""'<« 2, 

en O ^ 
C8 ^-' bo 

g e'C 


- c 


<^_^ en 

^ t-" ^y^ 

s 3 s 

*i CO CO 

C CO „ 

IS .— .^_^co -— 

s s H Sea — 






o o 


lO CO 

6 " 

CO 10 

O O O 1-' - CO 

CO Tt< O " CO CJ f^ 

io " 6 6 CO 1^ CO 

r^co CO CO CO tri r^ 

o w 

« "CO CD 


« - 6 io 

1 I 1 1 1 



10 1 C< CO K 


i-i 1 W -^ O) 

1 1 T^ 9^ 
1 1 ■^ co^o 

►H 1-C k. 




lO lO 
1 CO CI "O >*, 



1 CO " CO CO 


C u . . . . 

; (u _Q I- S : : ^ : : 

SfZ 2 cii o 

rt^i!'-' ^-5^2 O^ 

"CC ■^ O ^ -^ -^ •- 

= g^ g^.SpS^ |g g g 

K E >H 2; P5 o ph ffi 



o > C o o C 
3 O flj o 3 « 

„~ c" ^ „ ., 

^ PS 1; « ., r. 


- o y c! 







Elderton & Tildesley; and by Watson, Watson, Pearson, Karn, 
Irwin & Pearson. 

The division of birds into the two classes of nidicolous (those 
which hatch as squabs) and nidifugous (those which hatch as downy, 
feathered and active chicks) has been shown to extend to the com- 
position of their eggs by several investigators. Davy found that the 
eggs of the nidicolous birds had thinner and more fragile shells, 
which took up a less proportion of the weight of the whole egg than 
the shells of nidifugous birds. Thus the wren's egg-shell weighs only 
5 per cent, of the whole egg weight, while the hen's weighs lo per 
cent. Da\y's figures show very clearly that the main reservoir of 
solid is the yolk and the main reservoir of water is the egg-white. 

Tarchanov carried the matter further, and observed that the yolks 
of nidicolous birds always formed a smaller proportion of the total 
amount of material inside the egg than in nidifugous birds. Thus, 
for the former class the egg-white accounts for about 78 per cent, 
of the egg and the yolk for 22 per cent., while, in the latter class, 
the egg-white accounts for about 55 per cent, and the yolk for 45. 
All these differences are probably related to the shorter incubation- 
time of the nidicolous eggs; and, as will be seen later, there are not 
wanting indications that the yolk of these is less tightly packed with 
food-material and more rich in phosphatides. 

1*4. The Chemical Constitution of the Avian Egg as a whole 

The composition of the egg as a whole is further considered in 
Table 2, where it is noticeable that the analyses of water and ash 
have not been significantly improved upon between 1863 (the date 
of the first analysis, Payen's) and the present time. The later figures 
for protein and fat are, however, much the more reliable. It should 
be observed that there is an approximately equal quantity of fat and 
protein at the disposal of the embryo, though the former is, of course, 
in the yolk, and the latter is preponderantly in the egg-white. This 
protein-fat equality is by no means the rule in all eggs, and, as we 
shall see later, the eggs of fishes depart widely from it. There appear 
to be only small differences between the eggs of different kinds of 
birds in protein content. At one time it was thought that the duck's 
egg was particularly rich in fat, on the authority of Commaille's 
analyses, but Liihrig has since then brought it into line with all the 
others. It does seem, however, to have a considerably higher per- 





centage of mineral substances than the rest. The dry-weight figures 
merely demonstrate again the approximate equality of the protein 
and fat. 

Before we proceed to consider the parts of the tgg in separation, 
the question of individual and racial differences must be taken up 

Table 3. Individual differences between hen's eggs, 
Malcolm's figures (1902). Averages of individual hens. 

Breed unknown 

Italian hens (fed on maize and barley) 

From one hen 

From one hen 

Iljin's figures (19 17). 

Plymouth Rock 
Rhode Island .. 

itty acids 




















I 52 






















30- 1 2 







% dry weight 


Lecithin P 











59- 1 6 



Table 4. Race differences in hen's eggs. 

Leveque & Ponscarme's figures. 


% of egg d. 

"y weigh 



dry weight 



of whole 



N in 



i> 111 





in yolk 


Andalusia ... 














Bressane ... 







Coucou de Rennes 














Dorking ... 







Faverolles ... 














La Fleche ... 























O ■" 

WD "^ _ _,_ _^__ _.__ ,_^ ^_^__ __.__ 

J2 050 -^CTl m(N COOtD-r)"COOtDCO {S«30 I^ 

2 eD-*inTt<r^io<r>co co^p ^nto 'O'X) m coco in 

2t; CTio o-*' COM cni^ or~ cor^ tj-od co ct> <~~ ci 
"SS in^<N<o ocococo co«coo oeoip >oo co 
ccdo"'-"'-' Of" 6" "'-I "CI o<6 66c<" 

a a Tt>o com o<co into oci p~-o cocoot~- 
4j(00 lOCT) coio i-cio -^lO oco mmtD maii-i 

r^Mcoc^cooci 00)66 ctjo 6" 6<oicO" 
" cococococococow cococtcocococotxcoco 

i- o o o o o 


■53 oit^tico (r)f~-t6t6 trjLO ■ij-ti) (i> f^ t6 

i-i coco i^ CI 0^0 
V a><£) lo CT) t£> ■* 

rt (X) C£) CO •^ CT> K 


6 6 6 6 
mm mm 

o CO r^ o 

CTi r~- (T) ■* 

« en cicb 
m -^ ■* ■* 

- CO CO c< CO CI to 05C£) oieom'^'cici o ocor^ 

-fi CO CO CO CO CTlCO CO CT> CO O OiCO CD p r^ f^ O CO 

<6666 66 66 6« 66 6" 66«6 

ot; o-*ciTi-coococi ocicoci o^n coocor^ 
-O 2 f^ CI coco ►"t^mcTico'^cici cocna)coCT;co 

o o ■- " - 

o « o " o 


t^ m a^ o^ 

6 6 6 6 

00 00 00 00 00 

co-tomcomco"- otiD cicitoei 

u'v ci" cici Tfci 616 "6 i-" '*Tf<eo65-^ci 

d m ■^ 
■^ m 




r-to en 



^too ctjci ocicococimcirt" 
■J3 mcDi^o mci yh'Lnmcocir~- 
tt( in in 'J^ t^ mc£> ■^ m mt£i «6 m 

oi en CO CO CI CO 
CI 1^ CO 7*" 9 CO 
mt£> in ■* r^ m 

« o CO I- 
m CO CI m 

m-^cocotocotrsmcico r^eo" « 
en-* oiCT! coco mci too to o^mo 
inf^ 4fmtDf^!i>(o mf^^o ■^cnti 

^en-*toco cor-^eomoio ci'^'P';-' ci^Jcoi- 
"7, 66 r~f^«"Hi cimcocovoto 6<J>v6 r^" tj< 
Sh cococici •^coeocococococo'^eococi-^co 

< bo"_c cbCT)COco(i)cb r^m 
W> mmi£><o Tj-m mm 


CO CO CI M r-^ r^ CO 
' tJ< r^ 1- « to CO in 
1 m ■* m m -^vo m 

1=3 CTico r^ m 
_^ 6 oi coco 

P ^ 


•*tj< r-co cir~ r^mr-~ei 

66 cndici6)cicbci 6 





^ti m" ci-^ioto oeoto-cococi'+'enoci co 

^ -tj, mco t^"^ o^ m t^ •* oi t^ mco it* ci to r^ r^ to 

^•r; f^f^ 6 6 f^cb -^cb 1" ' 

P^^^-CICI "«" "-i-< ' 

to CO r^ t^ 

fiP'^'ij CI in r-«r^ 
W ^ > coco ^'^ 

d cir^-*0 r^O mi 

to « r^ CO 

CO-* CT)05 mm r^i-< •*" co coco ci 
6 ■* ineb 


S-^ oci mo p-Tj-t^o ■*'-' coo com-*omai 
djbCdr^mco cimcom mm mco ci r^ m m m m 
■^^tointoto inin-*-* into in -* 



in ■* to -^to 

mmi^f^ -^m -^m mto 

t3 G _ 

« o ^ 


« c o 

en o * CO 
m CO " m 

I p 2 


JS'.S 000 


c c 


O t^ CO 

M 3 


cS.ri COCO CO 

S w 6 6 6 













m m 


ri « 

C C 




to to 


-, n 

rf * 


w' 3 



" CO 


















CO to 


V <f 

0^ CO 



■* m 










1— 1 










u.^ CO Oito 

.Q I d^CT5 en 

J3 "& >^ o eo to 
K .SP C f^co t~« 
it^v-a^ ■- ■ ■ 

bo ? 








,..j5 !S o CO 

bc-^coto r- 

ll3 'C ,2 °^ en 

'^ > to m m 











<M 11 i-i (N « " 

O " O O 


coco CO =? ? T 

•<*"•*■* •* ■* T^ 


J3 b£ 

o o o 

in o o< 

o o o 

6 6 6 

6 6 6 

6 6 o 

w "^ « 







50 I 

w 5 

.SPI > .SP o > 

S J < £ !-!< 

jjoo-g uJoqSaq 

o « 

bc.-a ^ oitri <.o o ■:" IN CO 11 
"5 J? to in lo f^ f^ intis (6 


CO t^ <M CO r~« eo m 

^o o CO in o «r> 00 
f^to to f^ CD r^ ti 

CO OD CO CO 03 CO 00 

lite Yolk 
ght weight 

0503 05 01 '^ 1^ r^(£) 

coy3 ^ i^" ':' '^ <p^'-p 

O) CO r^tr> 
CO r^ o< O 

<^ m Oi 

in'-b in r^ in in -^^ 

ci f^ci) tr> 

(6 r^ to 

•* CT) Tj- m coco 1^ Tf 
■^ O) o uD c« O) inco 

o 05 mr^ 
■tf o ^ in 

05 in f^ 

Otp CO 


cococoo* cocococo 

tJ< CO ■^ in 


CO '^ CO 
coco CO 

V bO 

O CO i^co CO e* m >- 
tJ< tJ< Ln CO CO 05 r^co 

o t~- ine* 

N m CO 
o r^co 

Tj^eoin^ ineoiheo 

io -^ io 'Ji 

^in Af 



w 1 

ni-ii-tn COCOCOCO 

inminm mininm 

CO o •* in 
Of into i£) 

to into CO 
in in in in 

o in i^ 

into o 

incb r^ 
in in in 






Plym. Rock 
Rhode Island 
Plym. Rock 
Rhode Island 

Plym. Rock 
Rhode Island 



jqSjaM 3UIBS aqj 

paajq qoBS 

aOJ 33BJ3AY 



















o « 

U « C C O H 


ttj a./ 


CO NH CO *-• 

oi in in ■^ 
6 6 6 6 

(N 01 C< CO 

bl „ >-l » u 

ttl 01 1- ~ CI 


o r^ r~ r^ j~» 

•- to >- CO m 
ii CO O) ino) 
o ^ u ci (s 

« c( in in 

03 1~~ lO O) 

to to to f~- 
in in in in 

r- Oito J 
in O r}< j 

05 6 6 

'Z.^ <^ 

o o o o 

_j CO 

C O (U ►C 
V S •- . - 


again. Malcolm maintained in 1902 that, although there were un- 
doubtedly differences between the eggs of different breeds of hen, 
they did not exceed the amount of variation between individual eggs 
from hens of the same breed. His results are shown in Table 3. 
Thus, although the feeding was carefully controlled, the eggs 
from one hen might show a difference of i'i4gm. of fat, while 
between two eggs from different breeds the difference might be only 
0-13 gm. His conclusions were supported in the main by Carpiaux; 
Leveque & Ponscarme ; von Czadek ; Iljin ; and Willard, Shaw, 
Hartzell & Hole; who made very long studies of a considerable 
number of breeds. Some of the figures obtained by von Czadek 
and Iljin are given in Table 5. Von Czadek studied the Sulmtal, 
Minorca, Orpington, Rhode Island, Faverolle, and Wyandotte 
races, together with an Italian and a Rhineland breed. His outside 
values for egg weight, for instance, were 43 gm. and 75 gm. — 
a considerable difference — but the former was from the Rhineland 
hen and the latter from the Minorca variety. The span showed great 
variations, thus an egg weighing 55 gm. might be a heavy Orpington 
or a rather light Faverolle or a medium weight Italian. The only 
breed which stood well out of the range of individual differences was 
the Minorcas which laid very heavy eggs. Certain instances have 
shown, however, that remarkable agreement may exist between work 
done on eggs of widely different breeds. Thus the classical work of 
Plimmer & Scott on the phosphorus metabolism of the developing 
chick was confirmed very strikingly by Masai & Fukutomi, who 
worked in Japan. Here the correspondence was almost numerical. 
But on the other hand there is evidence that eggs of different breeds 
differ not only in their gross characteristics, but also as regards more 
subtle properties; thus Moran has demonstrated that eggs from 
different breeds of hen vary very greatly in their resistance to cold, 
so that the viability is different, and Needham, working on the inositol 
metabolism of the embryo, observed differences between the embryos 
from Black and White Leghorn hens. Physico-chemical differences 
between breeds of silkworm eggs are enumerated by Pigorini. 

The individual differences between eggs may be equally important. 
Benjamin has shown that there are numerous variable factors which 
modify the constitution of the egg. The amount of yolk, egg-white, 
and water, as well as the thickness of the shell, vary according to 
the season, diet, age (Riddle) and general condition of the bird 


in question. Nor are such comparatively slowly changing factors 
the only ones which bring about differences between individual 
eggs ; the time the egg takes to pass down the oviduct, for instance, 
will materially affect the amount of albumen it contains, and 
such variable quantities as the blood-sugar level (Riddle) and the 
level of cholesterinaemia in the parent animal will exercise their 
effects upon the resulting egg. Again, the length of time elapsing 
between the laying of the egg and the beginning of incubation will 
have a marked efTect, for a certain amount of water will evaporate 
from the egg-contents through the shell, and just how much does so 
will depend on the humidity of the surrounding atmosphere. The 
process of water-absorption by the yolk (Greenlee) from the white 
will also be affected by these conditions, so that the embryo at 
the initiation of its incubatory development may find a remarkably 
inconstant set of circumstances in its immediate environment. More- 
over, a certain amount of development always takes place in the egg 
after fertilisation as it passes down the oviduct, so that the embryo 
has already gastrulated by the time that the egg is laid by the hen. 
It was the ignorance of these facts which led Malpighi, as we have 
already seen, to his erroneous conclusions, for if he had known of 
the phenomenon of "body-heating", as it is called by the poultry- 
farmer, he would not have put forward the preformation-theory, and 
the eighteenth century would have been spared the trouble of getting 
rid of that embryological phlogiston. Thus no two eggs are ever 
exactly the same age, and as there is reason to believe that enzymic 
action begins in the yolk, if not in the white, very shortly after 
fertilisation, this fact makes it additionally difficult to get precise figures 
for the constitution of the unincubated egg. Then the position of the 
egg in the clutch (whether first or second) in pigeons may, according 
to Riddle, make a difference of 9-15 per cent, in yolk weight. It 
may be concluded that nothing short of the greatest caution must 
be employed in the material which is used for chemico-embryological 
researches on the hen's egg. The individual hens should be marked, 
and the eggs produced by them should be noted, their food should 
be constant in composition and the breed used should be not only 
single in any one series of experiments, but also, if possible, genetically 
pure. It is very greatly to be wished that standard hens could be 
obtained, such as the standard rats necessary for feeding experiments, 
and much further work, with a proper statistical backing, is needed 


on the range of individual and racial variations in all the properties 

of eggs. 

The effect of the diet of the hen on the chemical composition of 

the egg has been studied by various workers, notably by Terroine 

& Belin. Except in certain respects, it showed a remarkable fixity 

of composition : 

Table 6. 

Ordinary Corn and potato Hemp seed 
mixed ration almost ration 

ration free from fats (fatty) 

White in % of total weight ... 56-7 54-3 — 

Yolk in % of total weight ... 31-3 34-0 33-2 

Shell in % of total weight ... 11-4 lo-g — 

Water % 87-8 87-4 87-4 

Ash% 0-49 — — 


Water % 49-9 50-33 50-99 

Ash% 1-48 — — 

Total nitrogen % ... ... 2-67 — — 

Total fatty acids % 28-4 26-6 2655 

Unsaponifiable fraction % ... 1-85 — 2-08 

Cholesterol % i-i8 1-58 i-ii 

Lecithin P % — 0-425 0-434 

Thus, although the character of the substances stored for the use 
of the embryo can be varied considerably, as will be seen later, the 
balance of them cannot. But the question is probably rather com- 
plicated, for it has been shown by Dam that by feeding hens on a 
ration rich in cholesterol, the cholesterol content of eggs can be in- 
creased from 501 to 615 mgm. per cent, of the wet weight or roughly 
by 22 per cent, of the original value. In another instance the 
cholesterol rose from 476 to 560 mgm. per cent. This would not be 
in disagreement with Terroine & Belin's figures, but it would be 
a very desirable thing to make a detailed study of the limits of 
variation of all the constituents of the egg, and to find out exactly 
how different in chemical composition an egg can be from the normal 
while retaining its hatchability. Klein regards the cholesterol output 
of the hen in its eggs as showing a synthesis of that substance in the 
parent body. Leveque & Ponscarme have stated that it was not 
possible to show any effect on the eggs in eleven breeds of hen by 
minor variations in the diet; and this was amply confirmed by Gross. 

The ingenious and partially successful attempt of Riddle and 
Behre & Riddle to make hens preserve their own eggs by feeding 
them with hexamethylenetetramine, sodium benzoate, and sodium 


salicylate, may here be mentioned. Starting out from this practical 
suggestion the work led to the discovery of a number of specific 
effects of substances such as quinine on egg size and yolk size. Thus 
Riddle & Basset found that alcohol markedly reduces yolk size in 
pigeons, Riddle & Anderson found that quinine reduces egg size, 
yolk size and albumen size but has no effect on the protein/fat ratio 
of the egg, while Behre & Riddle found that the diminution of 
albumen size under quinine bore more on the solids than on the 
water and involved considerable reduction of the protein. 

The elaborate investigations on the egg of the tern, already 
mentioned, led to a significant correlation between abundance of 
food and size of egg, and it is certain that the size of the hen's egg is 
affected by its diet since the work of Atwood. There seems also to be 
a seasonal fluctuation, the weight of the eggs increasing from July 
to February and decreasing from March to June. These seasonal 
fluctuations appeared distinctly in Atwood's data, and explain the 
results of Curtis and of Fere. Rice, Nixon & Rogers and Riddle 
found a definite relation between the amount of food consumed and 
the number of eggs produced, both of these factors varying exactly with 
the seasonal variation in the egg size. Fluctuations of a regular kind 
seem even to occur each month, according to Hadley who observed 
such changes in egg weight and number. According to Curtis the size 
of the eggs increases as the laying bird matures, in the case of the hen, 
and Pearson has observed similar variations in the case of the sparrow. 

The genetics of egg production have been studied by Pearl and 

The relation between the egg weight and the chick weight at 
hatching has been studied by Halbersleben & Mussehl and by 
Iljin. The former workers found a quite consistent relation within 
one breed between the weight of the egg before incubation and the 
weight of the chick at hatching, the latter averaged 64 per cent, of 
the former. After thirty-five days of post-natal life, however, the 
slight advantage possessed by the chicks from the heavier eggs had 
altogether disappeared. They also noted that, other things being equal, 
chicks hatched from the more pigmented eggs (browner) weighed 
slightly more than those hatched from the less pigmented ones. 
Abnormally large and abnormally small eggs did not hatch as well 
as those of medium weight. Iljin collected a great many figures but 
his text contains no statistical analysis. 


Stewart & Atwood reported that chicks hatched from pullet eggs 
were neither so large nor so vigorous as those hatched from the eggs 
of hens two or three years old. Whether there is here a direct effect 
on the chick of the age of the hen, or whether the effect is indirect, 
due to the small size of the egg, may be well questioned. 

What relations exist between the chemical constitution of the egg 
and the percentage "hatchability" are at present obscure, owing 
perhaps to the comparative crudity of our estimation methods. The 
work of Pearl & Surface indicated definitely that differences in the 
hatchability of eggs are determined by or associated with innate 
differences in the individual hens which laid them, that these dif- 
ferences are probably inherited, and that variations within rather 
wide limits in certain environmental factors, e.g. the temperature, 
during incubation, are of secondary importance in determining the 
death or the hatching of the embryo. Hatchability of embryos would 
appear then to be, like fecundity, a heritable character. The experi- 
ments of Lamson & Card confirmed the conclusions of Pearl & 
Surface, but although some physico-chemical mechanism is un- 
doubtedly at work, these statistical studies gave no hint as to its 

Dunn determined to probe further into it. In his first paper he 
argued that if hatchability was associated with constitutional vigour, 
it should show a correlation with such a value as the chick mortality 
in the first three weeks of post-natal life. Experimentally this was 
not the case, e.g. post-natal mortality remained the same, although 
in two instances the pre-natal mortality was on the one hand ex- 
tremely high (20-39 per cent, hatchability) and on the other hand 
extremely low (80-100 per cent, hatchability). It therefore seemed 
likely that mortality before and after hatching is determined by quite 
different factors. The more specific influences operating in embryonic 
life must doubtless be looked for in the physico-chemical constitution 
of the unincubated egg. 

Hays & Sumbardo, in a search for such influences, were able to 
exclude statistically fresh weight, length, diameter, specific gravity, 
shell thickness, outer and inner shell-membrane thickness, porosity 
and imbibition of water from 25 per cent, salt solution. Other factors 
which have been excluded are percentage of protein in the diet of 
the laying hen (Rosedale), percentage of yolk-pigment (Benjamin), 
evaporation rate of the egg (Dunn), yolk-fat percentage (Cross), egg- 


fat percentage (Cross), yolk-protein percentage (Cross), egg-protein 
percentage (Cross), egg-phosphorus percentage (Cross), chick- 
phosphorus percentage (Cross). 

It appears, however, that the constitution of the egg-proteins may- 
be influenced by the presence of unusual proteins in the diet of the 
hen, and that this may influence hatchability. Pollard & Carr have 
reported the results of feeding the following proteins to laying hens : 
wheat, rye, corn, oats; kaffir, barley, peas, soya, hemp; buckwheat, 
popcorn, sunflower seed. 

The first group of four (all, of course, being fed alone) were very 
efficient for the production of normal eggs; the second group (of 
five) permitted the hens to lay eggs but the eggs were hardly hatch- 
able at all, while the third group allowed of no eggs. Pollard & 
Carr studied the egg-proteins in all cases and obtained evidence of 
tryptophane deficiency in the second group, so that they concluded 
that a minimum tryptophane content was essential for successful 
development through hatching. It is unfortunate that their results 
were never published in full. 

The effect of sex on the chemical composition of the egg has been 
discussed by Riddle. As is well known, in some, probably most, 
animals, the male produces two kinds of spermatozoa which are not 
equal in their prospective sex value, i.e. some which will give rise 
to females and some which will give rise to males. In birds, on the 
other hand, the dimorphism of the germs exists not in the spermatozoa 
but in the egg-cells. The female produces two kinds of eggs of unequal 
prospective sex value. Riddle found that pure wild species of doves 
and pigeons were ideal material for studies on sex, since very abnormal 
sex-ratios could easily be obtained from them, and his studies led 
him to the view that sex was more a matter of metabolic level or 
rate of protoplasmic activity than anything else. But what concerns 
us here are the consistent differences which he was able to demon- 
strate between male and female eggs. 

Pigeons generically crossed, when not permitted to lay many eggs, 
produce only males, but when made to lay many eggs produce first only 
males, and eventually "under stress of overwork" only females. These 
facts and their proper conditions having been ascertained previously 
by extensive statistical investigations, the way lay open for the 
chemical analysis of the two sorts of pigeon's eggs. 900 analyses 
were made and more than 12,000 yolks weighed. 



[PT. Ill 

Fig. 14, taken from Riddle, gives the differences diagrammatically. 
A glance at it shows that the male-producing egg of the spring 
contains less stored material than the female-producing egg of the 

Sex conbrol and known correlations in pigeons 



d cf cT d* cT ^ $ ^^ *? *$ ^9 •.>' ^ •-': "■ 

9 10 11 12 13 14 

N? 1 

N° <2 

N° 3 

N9 4 

N? 5 

N° 6 

N? 7 

N9 8 

N° 9 



N0I. shows comparabive size of eggs of Alba (A) 
and Orienbalis (0) 

Fig. 14. 

autumn. The amount of water and ash present, on the other hand, 
diminishes, and the rise indeed is mainly to be seen in the fat and 
lipoid fractions and in the calorific value. Table 7 gives the figures 
for one individual pigeon during 191 2. The differences are not 

SECT. l] 



large, but they were invariably found. Another series of figures show- 
ing the rise in calorific value during the course of the year and the 
transition fi-om male to female eggs is given in Table 8. Here also 
the increase is unmistakable. Within one clutch, also, the water- 
content of the second egg is lower and the calorific value higher than 
the first egg, which fits in very well with the fact that under normal 


May 26 


June 7 



July 3 











Table 7. Effect of sex on pigeon's eggs. 

Female Turtur orientalis x Streptopelia alba, no. 410 for 191 2. 

% wet weight % dry 

Analysed Weight t ^ ^ weight 

or in- of Pro- Extrac- ale- Calories 

cubated yolk Lipoid tein tives Ash Water sol. per egg Sex 

An. 2-330 18-32 25-44 5-28 4-85 5701 72-65 7405 — 

An. 2-660 17-54 25-63 5-25 2-62 54-82 72-45 8990 — 

Inc. — — — — — — — — Male 

Inc. — — — — — — — — Male 

Inc. — — — — — — — — Male 

An. 2-026 16-49 26-00 3-63 2-43 56-05 71-95 6714 — 

An. 2-330 19-18 26-55 3-75 1-93 5522 72-27 7881 — 

Inc. — — — — — — — — Male 

Inc. — — _____ _ Male 

An. 2-422 17-82 25-88 3-82 I -80 55-84 72-42 8061 — 

An. 2-720 18-88 25-96 3-86 1-81 55-33 72-45 9296 — 

Inc. _______ _ Male 

Inc. — — — — — — — — Male 

Inc. — — — — — — — — Male 

Inc. — — — — — — — — Female 

Inc. — — — — — — — — Female 

Inc. — — — — — — — — Female 

An. 2-700 21-40 — — — 55-45 73-17 9323 — 

An. 2-715 21-63 — — — 55-39 73-02 9383 — 

Table 8. Eggs from the same female Streptopelia risoria (1914). 


Weight of yolk Energy in cals. 

June 6 










I -000 


July 14 






Aug. 30 



Nov. 6 












Dec. I 



















conditions the first egg laid nearly always gives rise to a male and the 
second to a female. 

In Fig. 14 the line marked "developmental energy" implies that 
a higher percentage of the male eggs hatch successfully than of the 
female eggs. The data for length of life show the same curve. The 
smaller eggs of both clutch and season are the eggs which give 
positive results in strength and vigour tests, and the larger eggs are 
those which are liable to display weakness. These facts are in entire 
accord with the higher metabolic level which Riddle associates with 
the small male eggs. It is interesting to note that Lawrence & 
Riddle found consistently higher values for total fat and total phos- 
phorus in the blood of female fowls than in that of male fowls, from 
which they concluded that the metabolic differences between male 
and female germs persist in the adult, and all these facts are in agree- 
ment with the work of Goerttler and Baker on human and Smith on 
crustacean blood-fat, and of Benedict & Emmes on sex differences 
in basal metabolism. But for further discussion of the metabolic 
theory of sex, the papers of Riddle must be consulted. Interesting 
data on the hatchability, vigour, etc., of rotifer eggs are contained 
in the paper of Jennings & Lynch, but these authors made no 
chemical experiments. 

To say, as Riddle does, that there are, as it were, two kinds of eggs 
in some species, one male-producing, and the other female-producing, 
may either be taken to mean that there are quantitative differences 
between them or that their constituent substances are qualitatively 
chemically different, or, thirdly, that the same substances in the same 
quantities are differently distributed spatially and temporally. As will 
be seen later in connection with the lipoids of mammalian egg-cells, 
the second view finds supporters, and some such opinion is held 
by Russo. Faure-Fremiet, in the course of his work on the egg of 
Ascaris megalocephala, to which he applied every conceivable method, 
examined a very large number of individual eggs in order to find 
whether they separated at all chemically into two types. His method 
was to centrifuge them separately, much as McClendon had done 
with the frog's egg, and then to measure in mm. the thickness of 
{a) the mitochondria layer, and {b) the fatty layer. Fig. 15 {a) taken 
from his paper shows the frequency polygon which he constructed 
on the basis of these results, the ordinate giving the number of eggs 
measured, and the abscissa the thickness of the mitochondrial layer. 

SECT. l] 



It is quite evident that there are not two modes on the line joining 
the points, i.e. that there are not two types of eggs, but only one type. 
Faure-Fremiet made very similar experiments, determining the gly- 
cogen content of the eggs histo-colorimetrically with iodine solutions, 
and there also the frequency polygon had but one mode (Fig. 15 (^)). 
But this second case was based on an unsatisfactory method. In the 
particular instance under investigation, neither mitochondria nor 



12 3^5 




J : 

<k 5 7 8 

Fig. 15- 

glycogen happens to be an entity which varies as between the two 
kinds of eggs. Nevertheless, the plan of work was an interesting one, 
and widely extended researches with it, using accurate chemical 
methods, would be very desirable. 

1-5. The Shell of the Avian Egg 

Litde attention has been paid to the shell of the bird's egg from a 
physiological point of view. The relevant analyses are given in 
Table 9. There is some difference between the shells of different 








o o 


• rt £-< tJ-* 1-H 

^ OCO « 

B S 

S ^ 


3 --^ 



m g . 

U " 3 
. -1 ^-^ u 


^ ^ 



g a 

I I 

in CO ■* 

" I~» CO 

6 6 6 

in-*iininTj<co,coinc«oeoor^ CT) 








CO mco 


o o o 



CO t^ -* 




I I 

r-» CO tJh o^cd o CO oj f^ tjh a> 

CoiOTf<f^-^" COlOCOtj^C^ 


' Um 

e o u 

(U O 3 



• •^ 


C C >- D 

5 s i! 

b ^ 3 

O C O c 
O U 3 « 



. . T5 i-i . . . . 

. . g i) . . . . 

• • Q-a • • • • 

o g 

P 2 

«1i I 

4) o O S it( 
t^ O « !;< 

c !- 'y ,0 



3 II 

SECT. l] 



birds, and it would be interesting, for example, to know why the 
pheasant's contains such an unusually high percentage, of phos- 
phorus, and why the herring gull's has so high a percentage of organic 
substance. A certain interest attaches to the determinations of 
Balland on ostrich eggs, some from a tomb 
of the Hellenistic period and others from 
modern ostriches, but the differences he 
found were probably not very significant, 
as the analysis of Torrance seems to give 
values half-way between those of Balland. 
Neither Balland, Torrance nor Wicke states 
whether the ostrich used was the North 
or South African variety, a complication 
which might make a difference. Wicke 
believed that the difference in shell-com- 
position between different kinds of birds 
was almost entirely dependent on their 
usual foods. 

The microscopic structure of the shell 
was investigated by Nathusius in the 'sixties, 
and since then little has been added to his 
work. The shell consists of an outer layer of 
crystals of calcium carbonate arranged with 
their long axes perpendicular to the bound- 
ing surface (Fig. 16), and an inner layer 
composed of undifferentiated calcium car- 
bonate (Herzog & Gonell). Kelly; Schmidt; 
Meigen and Osawa have found that the 
mineralogical form of the lime is invariably 
calcite, no aragonite being present in any 
bird's egg-shell. This has been confirmed 
with X-ray analysis by Mayneord. The 
ostrich, Emj>s europaea, is the only doubtful case, for Kelly identified 
its egg-shell lime as conchite, but Torrance considers it to be calcite. 
Prenant's review should be consulted for further details regarding 
this interesting biochemical problem. Only one paper exists dealing 
with the changes which the shell undergoes histologically during the 
development of the chick; it will be considered in the section on em- 
bryonic respiration, where the data we possess on the question of the 
NEi 17 

-^:- -;>.,«■ j 

Fig. 16. a, Outer crystalline 
layer; b, c, d, amorphous 
layers; e, mamillae; /, shell- 



3co ^ 

Ss ll«5 In 


I I I I 



I I I I I I I M I iSalsi I I I I I I i|:m 1 I I m 
fji^lli I I El!" f I I '|i 1 I I I I i| 

I I M ill \^f\l I I I I lsf?l II? 1 I I I I I 111 if 


' I I I ?.j 

1 II ?i 

IS I I I I I ; 
^'i I 1 I 1 1 ' 

I °^ 

'? ll 

11 gl§'S! 

i^loo 11 loll 5 ol°"'^lllo 00 Oc^OO^SO «■« 


III 1 1 M i 1 1 1 iiii g°Eir^R 

ii|l 1 1 l|l 1 1 f I II I I I I II 

|l 1 1 II l|p|l I I I I I I I I I I 

'Hl.^ltli 1 1 i^ s' 6 s" MINI 

I i If I |||S|.| 
O I g 3 .-3 iiS5^^i£^ 

■ ^o 6:2 8 s-vgsra 

S § SO gOidpiCCK 
H Q Q O ( 



1||| I =1 

"■0 ^ ^'g 

"m "CS" 



1 1 1 1 

1 £l 1 1 

.-s -I 



permeability of the shell and its membranes will also be dealt with. 
There has been some controversy on the subject of whether the egg- 
shell contains any elements of the secreting organ in it, like the decidua 
of mammals. Von Baer thought not, but the presence of cellular 
structures has been reported by von Hemsbach; Landois; and 

The shell-membrane has been studied chemically by Liebermann 
and Lindwall, who found that it consisted almost entirely of a protein, 
the percentage composition of which agreed very closely with keratin 
(Table loa). Krukenberg, alone, on the ground of its reactions, held 
it to be a mucin. This ovokeratin, which contains four times as much 
sulphur as the albumen of the egg-white, was found by Morner to 
include 7 per cent, of cystine, but there are reasons for supposing 
that this figure is much too low. Nothing is known of the part 
played by ovokeratin in embryonic metabolism, but, in view of the 
fact that calcium is transported from the shell to the embryo during 
the period of ossification of embryonic cartilage, it is not impossible 
that the sulphur or the cystine of ovokeratin may be made use of 
in a similar manner to meet the need for sulphur and cystine 
for the feathers. This will be discussed later under the head of 
sulphur metabolism (Section I2'7). Morner considered that sulphur 
must exist in the ovokeratin in other forms besides cystine, for that 
amino-acid would not account for more than a third of what he found 
was there. The amino-acid analyses of ovokeratin are placed in 
Table 1 1 ; they are due to Abderhalden & Ebstein, and to Plimmer & 
Rosedale, the former by isolation and the latter by the van Slyke 
nitrogen distribution method. The arginine figure is rather high. 

The strength of the shell is clearly an important biological factor : 
according to Romanov its average thickness is 0*3 11 mm. giving a 
breaking-strength of 4-46 kilos. The relation between shell-thickness 
and breaking-strength is a straight line. 

The physiological properties of the shell of the bird's egg have been 
very insufficiently studied. In the last century there was a general 
impression that the shell possessed a differential permeability and 
that, while water and other liquids would readily go through the 
egg-shell and its membranes from outside in, they would not easily 
pass from the inside to the outside. It is difficult to find how this 
idea originated; thus Ranke in 1872 attributed it to the younger 
Meckel, and Ranke's own statement was subsequently copied down 


: siuaQ ^ ujio^ 

aioonwoAO :-i3ii3Z 

: bu3uno3nj-j 

V V 
t-, S-. 

lOM lO t^ t^ CT) J^ 

'-' <-o 6 6 6 6 ,'-' 

NIHSVD :u3piEqjapqY 

CCTlOLOi-iiNar^iNuOO lOCC cc 


:s3uof jj sujoqso 

puB jqosjinBjg :§ 

qwo.wusABsq 'auioqsQ 


NmaxiAOAO M o ^^ o coco m ci 

:(3uiui3jb) uipaH pue ;-|2e»«cooi6w 

jajunjj 3? uspjBqjapqv fn "" " 




X3 D. 

E £^' 




aiDV oiNiaivsAq 

aiDv aiNiaiYioad 


4. (psjBinSEOo) NHIMiiaiV 
-OAO : (auusXD) jaujoj/v[ 
puB pjoi\ib§ buaunoSn]^ 

" I o CO o 
« I 6 6 -^ 

o c< , o 

O O CO ^J* 
c( cj ,1, I CO 

CO ■^ CO 

c< 6 CO 

CI «- 


CJ 1^ lO 

CD 'f 


m - 

LO " CO 


uO CD C^ 

1 ?-^l 1 


" CI CO 

' 6 t- ' ' 


^^(pasTiiBjsiUo) NHwriaiv v q 
-OAO :u3piBqj3pqy puB g « 
jSajj ^ uap]Bqj3pqv 2; =0 

t^ CI tJ* — CO 


-jeisAjo) NraiMnaivoAO 
luaqjiQ Jg aujoqsQ puB 
q;jOA\u3AB3q 7g sauof 
'sujoqsQ ijqoapnsjg 3g 
qUOA\U3AB3'7 '3ujoqso 

M 01 O CO lO CI CD 

>- " O ■* CO " 
r^ C) r^ CO CI ^ 

« t}< CO " " ,1^ 


: : : : :'S o cs : : : : : .S E u S 2 o 

V V V „,'rt.yS c <u c g "c rt gH-S;^ s g.2 
.S.S y.S c^ti i o-S g-^-g li § S 2 £2^ § t3 
G S-S u-^ c rt S c o-s-^.S.S £ o a-o'rtls (^ « 

>^c3-i33o«CI.3-r;SHMc/,b0vic3 >-"e -^ -i^ n (i: 




I I I I I I I I ^1 I I I 

: uapjBiiaspqY 

O 7J"Ocp o 


: pjBUlIIBQ 

jj buaunoSnjj 

: 3U}3{j 3g UBUideqQ 


; SjaqsjY ^ auaAsq 

c T « 

' rsi 

r (3>i^is 


UBA) aioonivoAO 



(35lXlS UBA) 















-oaj aiiH.\\-003 

(ajjXis UBA) 

o o o o o , o 

CO O OtX> O 7** 

eoTj^i. 6 " 6 

6 " 

CO a> ;*• 

I I 

CO 'f CT) 





















:^ 1) 

t^ CO 


Ph sh 

C< Tf 


T ^ 



t^ !N 



o e< 





'in O 

01 r-^ 


M t« 

c< o 

« « 



r^ c< 




-]pqs) NI1VH3M0A0 

: (aupsAo) j3ujoj\i 

puB uiajsqg 

^ uapjBqiapqy 


?^ 9 

UBA) SNiaioHd-ooa 

aaxiw :s3puMoq 

^ jauiuijitj 

+ o + 11 
CO -^coo 1 1 

' ' CO o 


« o Th« 

LO •+■ 


.s.s H.S s->-g i 

>-nil5 j^ O W Dh_3 



I I 

LNaiMiiaivoAO I i I I I I I I I 

I I 


I 1 I 

I I 1 ?. I I 1 I 

: (suusXo) uBAT^ng 
puB (auBqdojdXai) 

1 I I I I I l|l I I I I r I 

NHwnaivoAO ^ 



e-6 i u i •: I 1 1 1 1 1 1 I I I 

!r> CO 

o ^f 

lO - 

I r. 

I I I 1 1^ I I I I 

: UOU1051 


aaxiw :3duiax ■„ I 
28 uapieqjapqv 


-OAO :s3UJ30H 

jg jauiBSuapv 

o 3 n m 


aaxiiM :nfpu3S 

to o» a ■* 1^ 


-U3AB3T 'aujoqso 











osine ... 
tine ... 





identified £ 
al di-amin 


S 6 
— t« 








wrongly by Schafer. However, Thunberg in 1902 conclusively 
demonstrated the error of the belief, and showed experimentally 
that water would pass through the membranes equally well both ways, 
though he found that of the two the inner one was the less permeable. 
In the case of water birds, there is evidence that the shell is absolutely 
impermeable to water; Loisel, for instance, found that the eggs of 
the grebe, Podiceps cristatus, and the duck, Anas domesticus, when 
placed in distilled water absorbed not a trace of it, and gave out 
no chloride to it over a period of many hours. The eggs of the 
ordinary hen, on the other hand, increased considerably in weight 
and allowed some chloride to pass out into the water. At the same 
time, Loisel found that hen's eggs develop quite normally, at any 
rate up to the seventh day, even if they are lying in water. This 
experiment of Loisel's was confirmed by Lippincott & de Puy, who 
succeeded in hatching chicks from eggs incubated while lying in | in. 
of distilled water. The differences between these eggs and the controls 
suggested that the eggs lying in the water not only failed to lose as 
much water through evaporation as eggs incubated under ordinary 
conditions, because of the limitation of the evaporating surface, 
but actually absorbed some water. Trials with rhodamine red and 
methylene blue demonstrated penetration by these dyes, extending in 
the former case to vital staining of the embryo. It is known (Rizzo) 
that the avian egg-shell has many pores (o-86 to 1-44, average 1-23 
per sq. mm.). 

As regards gases, the only paper is that of Hiifner. Hiifner placed 
small pieces of egg-shell with their membranes in a diffusiometer, 
and measured the rate at which gases passed through the obstacle. 
He found that oxygen diffused through with most difficulty, then 
nitrogen, then carbon dioxide, and, finally, hydrogen most easily. 
It may be significant that carbon dioxide would thus appear to be 
able to escape somewhat quicker than oxygen can enter. But under 
normal atmospheric pressure the amount diffusing through the whole 
egg-shell (goose) per second was 2-115 c.c. of oxygen and 0-503 c.c. 
of carbon dioxide. The diffusion velocity was always proportional 
to the partial pressure of the gases, and the removal of the inner 
membrane made no difference at all, suggesting that the principal 
barrier was the amorphous calcium carbonate layer. It would 
be very desirable to repeat these observations with more modern 
methods, and on a greater variety of eggs. 


1-6. The Avian Egg-white 

The white of the egg is divisible into three portions which have 
been studied separately by Romanov. The outermost and thinnest 
layer makes up 39-8 % of the whole and has 1 1'6 % dry solid. The 
middle layer accounts for 57-2 % and has 12-4% dry solid, and the 
innermost, thickest, layer is only 3 % and has i4'5 % dry solid*. The 
chalazae have only once been analysed separately (Liebermann), 
when the elementary composition of their protein was ascertained. 
Table 1 2 summarises the results of the investigators who have made 
general analyses of the white. It is a very watery solution of 
protein, containing only the most negligible traces of fats and 
lipoids, but a great many water-soluble substances such as carbo- 
hydrate in various forms, protein breakdown-products, choline, 
inositol, etc. Natural egg-white, according to Rakusin & Flieher, 
is a saturated solution of ovoalbumen (15-35 P^^ cent.). The 
water-content does not vary much, but Tarchanov's analyses go 
to show that the smaller eggs with short incubation-time are 
wetter than the others. The proteins of the egg-white are believed 
to be variable in number in the eggs of different birds. In that 
of the hen, four are known, in that of the crow three, and in that 
of the dove one only. The egg-white of the hen's egg contains two 
albumens, ovoalbumen and conalbumen, and two glucoproteins, 
ovomucoid and ovomucin. 

It was at one time thought that there was a fifth, ovoglobulin. 
Dillner studied it in 1885, and estimated that it made up 0-67 per 
cent, of the egg-white and 6-4 per cent, of the total protein, but 
Osborne & Campbell showed that it was simply a mixture of the 
others in different proportions. This had already been made probable 
by the results obtained by Corin & Berard, who were able to separate 
the ovoglobulin into two or three constituent proteins having 
several different coagulation temperatures (57*5°, 67°, 72°, 76° and 
82° C.) and other special characteristics. 

Hofmeister was the first to prepare crystalline ovoalbumen, and 
he published several papers on it. Other workers confirmed his dis- 
covery, such as Gabriel ; Harnack ; and Bondzynski & Zoja, but 
Hopkins & Pincus showed that the albumen so crystallised only 
accounted for half the protein present in the egg-white. Part of the 
missing protein was found by Osborne & Campbell to be in the 

* A large number of concentric rings can be seen in egg-white coagulated in situ, 
according to Remotti. 



[PT. Ill 

*2 U 

> B 

c ^ 

he- O 1) > 
•O O g :3 § 


a o 

tj> CO 

Ph O ■ - - 

(u D c u 2 9 o 



O ^Z,C^ CD " 

, e< ' > . ,„ n 

3 " 5-5 S cng ^ 

>-j >j= ^ to.c e £ 

Ki cij u .^ bc:^ tS i=! 

I I I 





'JD O — 
r^ I CO r- I I 

o I •* 
« ' CO 

O K3 COtO <ri CO CO CO K) 


— . O CO LO r^ 
f^ CO xi LOCO 
6 6 6 6 6 

o in 

o o 

O O 

^D^D I 4^ f^ 

O O 

? 2 u 
A ?^ =« 



r^tr> oco(NCOco, "^.cjoc* 

0(C)c<oooo 7" -^ p 
6666666 6 66 

" o 
6 6 


" oco 
x^ CO ■* CO 


CO lOtD 


!N CO 0» CO CJ 


- - « 


cr> 0!n 

CO 0)0 I^ ot 

CO t^UD 

M o -' o 6 


rS bn w 

C bo Q 
<fi u OS 

(0 D 


t, -2 c 


3 D W 



C3 Q^ ^ 

S"! K i-i 
c3 o « 



< 3 "=o 



.V HJ 













r- oi 


If I I I I I I I I I I i I I I I i I I ? 

OCO" 000000000 0000000 CI N 

cocTi^ «a>-<o~ciLOcoyf oito c~,co c~. o o c> o 

cococo cocococoo oico coco cocooococococococo 

o ^ ^ 

jn v X . t„ to 

u '^ 


Table 13. Distribution of proteins in avian egg-white 




Passeres (singing birds) 
Turdus iliacus 
Turdus piliaris ... 
Anthus pratensis ... 
Anthus cervinus ... 
Garrulm infaustus 
Corvus cornix 
Corvus nionedula ... 

Zygodactyli (2-toed) 
Dryocopus martins 

Accipitres (birds of prey) 
Strix aluco 
Falco gyrfalco 
Falco peregrinus ... 
Falco aesalon 
Falco tinnunculus... 
Astur palumbariiis 
Buteo lagopus 
Pandion haliaetiiis 

Pullastrae (doves) 
Columba livia 

Gallinae (fowls) 
Gallus domesticus 
Meleagris gallopavo 

Grallae (marsh birds) 
Charadrius apricarius 
Haematopus ostralegus 
Tringa alpina 
Phalaropus hyperboreus 
Totaniis glareola . . . 
Actitis hypoleiicos 
Limosa lapponica 
Numenius arquatiis 
Numenius phaeopus 
Fulica atra 

Lamellirostres (ducks) 
Anser segetum 
Fuligula marila ... 
Fuligula fuligula 
Oedemia fusca 
Clangida glaucion 
Somateria mollissima 
Mergus senator . . . 

% wet 


% of total protein 
in eg5-white 
















I "49 








and date 

Osborne & Campbell 

(1909), r^ 

Komori (1920) 
Needham (1927) 
Morner (19 12) 

— Morner (1912) 




Table 13 [cont.]. 

% wet 


% of total protein 
in egg-white 


ovo- ovo- ovo- 
mucoid mucin albumen 

and date 

Steganopodes (pelicans) 
Phalawcrocorax carbo 
Phalarocrocorax graculus ... 


2-o8 — — 

Mdrner (191 2) 

Longipennes (swallows) 
Larus cantis 
Lesiris crepidata ... 
Sterna macrura ... 
Sterna hirundo 



15-00 — — 


Pygopodes (divers) 

Podiceps cristatus 
Colymbus arcticus 


— — — 


form of the two glucoproteins and the other albumen, while part of 
it was accounted for by the fact that the yield of the crystallising 
process is not great. Ovomucoid was originally discovered by 
Neumeister, who called it "pseudopeptone", and first studied by 
Salkovski and Zanetti. 

The investigations of Osborne & Campbell, whose memoir is the 
best on this subject, give no very definite indication of the pro- 
portions in which these proteins make up the protein fraction of 
egg-white, but they put ovoalbumen at about 80 per cent., and 
ovomucin at about 7 (see Table 13). Later, Komori estimated that 
ovomucoid accounted for about 10-5 per cent, of the proteins, and 
in 1927 I obtained a figure of 7-6 per cent, for the same con- 
stituent. Morner, in his extensive study of ovomucoid in numbers 
of birds' eggs, obtained results from which higher figures emerge on 
calculation, namely, from 10 to 20 per cent. The only exceptions 
were the pelicans, which seemed to have very little ovomucoid. The 
most probable relationship between the proteins is as follows: 
ovoalbumen 75, ovomucoid 15, ovomucin 7 and conalbumen 3 per 
cent., but these values are only very approximate, and further work on 
this point is much to be desired. Leaving out ovomucin, Wu & Ling 
found that the proportions were as follows (for Gallus domesticus) : 
ovoalbumen 78-3, ovomucoid 12-3 and conalbumen 9-4 per cent., or 
1-34, 0-21 1 and o-i6i gm. per cent, respectively. Certain Russian 
workers (Worms and Panormov) have described two proteins, anatin 
and anatidin, in the egg-white of the duck's egg, and three, corvin, 


corvinin and corvinidin, in the egg of the crow. It is not certain, 
however, to which of the well-known proteins of the hen's egg-white 
these others correspond. Judging from the percentage composition 
tables in Table lo a, the columbin of the dove's egg corresponds 
to hen ovoalbumen and to duck anatinin, while duck anatin corre- 
sponds to hen ovomucin, but in the absence of definite information 
the question must be regarded as unsettled, and would repay further 

The minimal molecular weight of ovoalbumen, according to 
Cohn, Hendry & Prentiss, is 33,800 (Marrack & Hewitt suggest 
43,000), and its percentage composition is seen in Table 10 a; 
the best analyses are probably those of Osborne & Campbell, 
who give an account of its general properties. It has been further 
analysed by several workers who have determined the proportions 
of its constituent amino-acids, and whose results are seen in 
Table 11. The hydrolyses of Osborne, Jones & Leavenworth; 
Osborne & Gilbert, and of Abderhalden & Pregl were all done by 
acid, but those of Hugounenq & Morel and Skraup & Hummel- 
berger were alkaline, the former using baryta. The figures agree 
accordingly, and all that can be said of them is that for purposes of 
calculation the amounts of amino-acids must be taken as minimum 
in each case. Attention may also be drawn to the less complete 
analyses of Chapman & Petrie and Hugounenq & Galimard and to 
the analysis of mixed egg-white proteins by Plimmer & Rosedale, 
using the van Slyke technique. The large amounts of hexone 4Dases 
found by them contrast with those found by the remaining workers, 
using direct isolation, and if this is not due simply to difficulties of 
technique it may lead us to expect a high content of hexone bases 
in conalbumen and ovomucin when they come to be analysed. 

In Table 10 a the results obtained by Gupta on the hydrolysis pro- 
ducts of ovoalbumen are given (see also Rudd). It is noticeable in 
them, as in the analyses of ovoalbumen itself, that they contain 
a high proportion of sulphur, though not so much as ovomucoid. 
The spontaneous evolution of hydrogen sulphide by egg-white 
on standing has long been known, and was made the subject 
of a paper in 1893 by Rubner, Niemann & Stagnita, who found 
that 100 gm. of egg-white gave off when boiled with water 10-7 mgm. 
of HgS. Hausmann later decided that its source must be some labile 
sulphydryl grouping in the ovoalbumen molecule. In 1922 Harris 


observed that raw egg-white was quite non-reactive towards the 
nitroprusside test for sulphydryl groups, but that immediately upon 
coagulation by heat it became vividly reactive, and gave an intense 
purple colour. This change only took place in conditions where 
denaturation of the protein was involved, and Harris suggested that 
this treatment might unmask a thiopeptide linkage or some similar 
arrangement which by hydrolysis or keto-enol transformation would 
give rise to an active sulphydryl group in the resulting metaprotein 
molecule. Later, Harris found that only 14 per cent, of the sulphur 
in ovoalbumen could be accounted for as cystine, so that some un- 
known sulphur compound must be present in considerable quantity, 
and an exactly similar finding was later reported by Osato for the 
egg-membrane protein of the herring. The cystine recoverable from 
serum albumen, on the other hand, accounted for 86 per cent, of 
the sulphur there. The possibilities of these facts with relation to the 
metabolism of the embryo have not yet been explored. Philothion, 
according to de Rey-Pailhade, exists in the egg-white of the hen 
but not in that of the duck. 

The principal investigation of ovomucoid is that of Morner. He 
had previously discovered that percaglobulin, a protein extracted 
from the unripe ovarial fluid of the perch {Perca fluviatilis) would 
precipitate ovomucoid from its solution. With this reagent he made 
an examination of a wide variety of birds' eggs, in order to study 
the distribution of ovomucoid. By direct estimation he found it to 
be present in all the eggs he studied, but it seemed to exist in two 
sharply distinguished forms, one which would give a precipitate with 
percaglobulin, and another which would not. Thus the hen [Gallus 
domesticus) with i -46 per cent, of ovomucoid gave a highly positive 
reaction, but the hawk {Astur palumbarius) with i -45 per cent, gave 
none at all. Preparations of ovomucoid from the two varieties of 
egg-white (see Table 10 a) did not show up the existence of two ob- 
viously different chemical individuals, and it was concluded that the 
preparations were in each case mixed with a small amount of the 
other substance. Moreover, of the egg-whites which gave a positive 
reaction with percaglobulin, some contained ovomucoid precipitable 
with Esbach's reagent (e.g. Clangula glaucion and Somateria mollissima) 
and others contained an ovomucoid which could not be so pre- 
cipitated (e.g. Gallus domesticus and Podiceps cristatus). It is quite 
uncertain how many of the effects observed by Morner are due to 



[PT. Ill 

physical and colloidal rather than to chemical differences, and the 
whole question should be reinvestigated. There seemed to be no 
special significance in the distribution of the ovomucoid which was 
precipitable by percaglobulin ; thus it was present in the accipitres, 
grallae, lamellirostres, longipennes and pygopodes, but not in the 
passeres, zygodactyli, pullastrae and steganopodes. As for the fowls, 
it was present in the eggs of the hen and pheasant, but not in 
those of the guinea-fowl. Morner was inclined to agree with Milesi's 
view that ovomucoid did not exist as such in the natural egg-white 
at all. 

Table 14. Variations in properties of avian egg-white. 

Coagulation point 

Consistency and 

of the 

egg-white m 

colour of coagulum 

degrees Fahrenheit 



Hard white 




Pretty firm, bluish 



Soft, white, translucent . 


Missel thrush 

Soft, transparent 



Firm white 



Soft white 



Pretty firm, greenish, 


Golden-crested wren 

Soft, bluish, semi-trans 


As has already been observed, Sir Thomas Browne was one of 
the first to note that the coagulated egg-white of the gull's egg was 
quite different in consistency and translucency from that of the hen's 
egg. In 1863 Davy collected some data on these points, which are 
shown in Table 14, and Tarchanov devoted much time to the 
question in the 'eighties of the last century. He found that the whites 
of many kinds of eggs would not coagulate in the ordinary way on 
boiling, but either remained liquid and transparent or else set to a 
watery translucent jelly. This he called " tataeiweiss ", and as he went 
on to examine the distribution of this property he found that it was 
associated with the hatching quality of the bird in question. Thus 
all nidifugous birds, whose chicks are born fully feathered ("downy") 
and soon leave the nest, had eggs with ordinary egg-white, but all 
nidicolous ones, whose chicks are hatched as "squabs" or naked and 
weak, and have some development yet to complete, had eggs with 
uncoagulable or transparent egg-white. Thus the sand-martin, linnet, 
finch, thrush, canary, crow, dove, rook, nightingale, robin, starling 
(roughly passeres and pullastrae), all had tataeiweiss] while the hen, 


duck, goose, guinea-fowl, partridge and corncrake had ordinary 
white. This classification agreed roughly with Davy's high and low 
coagulation points for the egg-white, and corresponded on the whole 
to Morner's two classes, the former having ovomucoid not precipit- 
able with percaglobulin and the latter having the precipitable 
variety, but to this there were some exceptions; thus the plover's 
ovomucoid could be so precipitated, but its egg-white was tata 
and it yet produced fully-feathered chicks. It was, however, the only 
exception to Tarchanov's generalisation, (It should be explained 
that the word tata was derived from the name of Tarchanov's small 
daughter.) Tarchanov found that tata egg-white was about 3 per 
cent, richer in water than the other kind, a conclusion which Morner's 
later analyses did not confirm. He also said that it was alkaline to 
litmus, but became less so as the tata eggs developed. This agrees 
with the later classical work of Aggazzotti on the reaction of the egg- 
white of the hen's egg during its development. Tarchanov reported 
that tata egg-white could be made to coagulate at ordinary tempera- 
tures by the addition of a little potassium sulphate, and that it would 
itself coagulate if the temperature was raised well above the boiling- 
point of water. It was, he said, more easily digested by enzymes, it 
putrefied more readily, and during development it changed into a 
form resembling ordinary egg-white. He made some studies on its 
secretion by the oviduct of these birds, and was the first to perform 
the experim.ent of putting a ball (in his case a lump of amber) at 
the top of the oviduct and seeing it emerge at the bottom with layers 
of egg-white and a shell secreted around it. The change during 
development from tata to ordinary egg-white Tarchanov found he 
could imitate by bubbling carbon dioxide through the original white, 
after which it would coagulate in the usual way. On the other hand, 
he found that if he soaked normal hen's eggs in a 10 per cent, solu- 
tion of alkali the white took on the properties of tata egg-white, and 
became just like the glassy material in the sand-martin's egg. He 
suggested some relation between these phenomena and the alkali- 
albuminate of Lieberkiihn, but did little to determine its chemical 
relationships. He was unable to get any development in the case of 
hen's eggs soaked in alkali. 

In 1 89 1 Zoth took up the whole question of tataeiweiss once 
more. He was led to do so on account of some researches which he 
had been making on the effect produced on serum-clotting by various 


concentrations of alkali, and which showed that the clot could vary 
very greatly in its properties, from opacity to almost perfect trans- 
parency, for instance. Tarchanov had decided that the transparent 
coagulum of the nidicolous egg-whites was not to be identified 
with that produced by sodium or potassium albuminate, but Zoth 
succeeded in showing that the differences were not sufficient to dis- 
tinguish them. Zoth fully confirmed Tarchanov's finding that ordinary 
egg-white could be made to pass over into nidicolous egg-white by 
treating it with i o per cent, potash in the cold for ten days, and was 
able to explain all the differences between tataeiweiss and alkali 
ovoalbuminate as due to variations in the amount of alkali present, 
or rather the amount of cation as compared to anion. It is most 
unfortunate that we have no detailed ash analyses of the egg-whites 
of nidicolous birds, for, as will later be seen, the egg-white of the 
hen has rather more total anion than total cation, and this relation- 
ship might be expected to be even more strongly marked in the case 
of nidicolous egg-white, perhaps^ indeed, as much as to counter- 
balance the excess of cation over anion in the yolk. There can be no 
doubt, however, that the egg-whites of nidicolous birds are relatively 
richer in alkali than are those of others, and it is this, combined with 
their different water and total ash content, which causes the albumen 
to coagulate differently from those of others. Thus, if 5 c.c. of filtered 
egg-white from a fresh hen's egg be put in each of three small 
Erlenmeyer flasks, 2 c.c. of water added to A, 2 c.c. of 0-89 per cent. 
KOH to B, and 2 c.c. of a mixture of equal parts 0-89 per cent. KOH 
and 0-66 per cent. NaCl to C, the coagulum in A will be the usual 
white, thick, solid and opaque mass, while the other two will be 
transparent like tataeiweiss, slightly opalescent, more or less liquid, and 
Cmore opalescent than B. It would be interesting to reinvestigate the 
whole question anew in the light of recent knowledge and technique. 

Another curious effect was noted by Melsens and Gautier. Melsens 
found that, if a stream of carbon dioxide, hydrogen, nitrogen or 
oxygen, was passed through dilute egg-white, or if it was shaken 
violently, a precipitate of fibrous membranous shreds was formed. 
Gautier observed that about i -5 per cent, of the protein was thus 
changed; he filtered it off and determined its elementary composition, 
which showed nothing remarkable. He concluded that a protein 
which he called " ovofibrinogen " existed in the egg-white, and even 
suggested that an " ovo thrombin " was present to turn it into "ovo- 


fibrin". He apparently thought that the ovofibrin was incorporated 
without change into the substance of the embryo. The subject has 
not received any attention since the time of Gautier, but it is probable 
that this phenomenon is explained by the work of Young; Dreyer & 
Hanssen and others, on the high instability of protein solutions. 

Peptones were reported by Reichert to exist in fresh egg-white. 

Wu & Ling have recently studied the coagulation of ovoalbumen 
by strong mechanical agitation. The fact that conalbumen is not 
coagulable by such means gave them a method of estimating it in 
egg-white. Thus they obtained the following figures for Gallus 
domesticus egg-white: 

Total N (ovoalbumen + conalbumen 4- ovomucoid) 1-71 gm. % 

After shaking (conalbumen + ovomucoid) ... 0-372 ,, 

After shaking and heating (ovomucoid) ... 0-211 ,, 

Coagulation of ovoalbumen by shaking was not separable into two 
stages (denaturation and agglutination) like that by heat or alcohol. 
The isoelectric point of the protein was the most favourable for 
shaking coagulation (/?H 4-8) and the Q^^q of the reaction was i-g. 
Piettre has published a method for separating the proteins which 
involves the use of acetone. 

The relationships between the avian egg-white proteins have been 
the subject of some interesting immunological work. The earliest 
investigators who crystallised ovoalbumen found that perfect fresh- 
ness was necessary, for at room temperature the crystallisable protein 
gradually turns into a non-crystallisable one. Bidault & Blaignan 
found that this process could be arrested by placing the ^gg at 0°. 
Sorensen & Hoyrup suggested that the protein formed was conalbu- 
men and wished to look upon the latter as a product of ovoalbumen. 
Hektoen & Cole, however, first showed that though ovoalbumen 
was distinct from the serum albumen of the hen immunologically, 
conalbumen was not, and then went on to demonstrate that during 
the loss of crystallisable ovoalbumen which takes place as the egg 
ages, there was no corresponding increase in conalbumen. We must 
therefore look upon the latter as probably identical with the serum 
albumen of the adult: and perhaps only present in the ^gg owing to 
the inefficiency of the oviduct. 

The analyses of ovomucoid and Eichholz's ovomucin, as well as 
the fragmentary one of conalbumen, will be found in Tables i o a 
and 1 1 . Willanen found that ovomucoid was much more susceptible 



to hydrolysis by pepsin than by trypsin (see later under enzymes and 
antitrypsin). For its properties see the papers of Morner and Neu- 
mann. Both the glucoproteins have twice as much sulphur as ovo- 
albumen. Their carbohydrate content has been the subject of a great 
amount of discussion and experimental work. Berzelius was the 
first to draw attention to certain similarities between the breakdown- 
products of sugars and proteins when acted upon by boiling acids. 
In 1876 Schiitzenberger asserted that the ovoalbumen molecule 
contained a carbohydrate group, basing his views on positive results 
with Trommer's test after total hydrolysis. In later years a number 
of workers supported the view that the carbohydrate was glucose, 
using in different cases methods of varying reliability, e.g. Kruken- 
berg in 1885, Hofmeister and Kravkov in 1897, and Blumenthal ; 
Blumenthal & Mayer and Mayer in 1898 and 1899. Spencer and 
Morner, however, failed to get any evidence of a carbohydrate 
group after hydrolysis, and reported their negative results in 1898. 
Weiss, about the same time, thought he could identify a methyl 
pentose among the hydrolysis products, but he was never confirmed. 
Seemann was the first to announce that the carbohydrate was glucos- 
amine, and his discovery was quickly confirmed by Frankel and 
Langstein. These later workers began to attempt quantitative estima- 
tion of the sugar, and their figures are given in Table 15. Pavy, 
using the then recently discovered osazone technique, made a study 
of a variety of proteins, and showed, as might be expected, that the 
yield from ovoalbumen was always greatly less than from ovomucoid. 
Eichholz obtained glucosazone from ovoalbumen, ovom.ucoid and 
ovomucin, but not from either serum albumen or casein. On the 
whole, it is most likely that ovoalbumen contains extremely 
little glucosamine, and the figures recorded in the literature for 
this are probably due to contamination with ovomucin. This is the 
view of Osborne, Jones & Leavenworth, for neither they nor 
Osborne & Campbell obtained any glucosamine from their very 
carefully purified ovoalbumen. Komori has prepared from ovo- 
mucoid, and Frankel & Jellinek from ovoalbumen, polysaccharide- 
like substances which they regard as the prosthetic group containing 
all the glucose. Following this up Levene & Mori have prepared a 
trisaccharide containing glucosamine and mannose from egg-white. 
Ovoalbumen contains 0-26% of this substance, coagulated egg-white 
1*9%, and ovomucoid 5*1%. According to Levene & Rothen the 

SECT. l] 



molecule consists of four trisaccharides each containing one molecule 
of glucosamine and two of mannose. 

Table 15. Ovoalbumen and ovomucoid glucosamine content. 

Hen {Callus domesticus) 

Hofmeister (1898) 

Seemann (1898) ... 

Langstein (1900) 

Willanen (1906) ... 

Pavy (1907) 

Samuely (1911) ... 

Neuberg & Schewket (1912) ... 

Zeller (1913) 

Needham (1927) 

Abderhalden, Bergell & Dorpinghaus 

Neuberg (i 901) ... 

Blumenthal & Mayer (1900) ... 

Izumi (1924) 

Tillmans & Philippi (1929) 
Turtle ( Thalassochelys corticata) 

Takahashi (1929) 

Bywaters (1909) Seromucoid 
Pavy (1899) Ovomucoid 













Glucose % by hydrolysis with 

Osseomucoid ... 
Tendon mucoid 
Ovoalbumen ... 
Serum globulin 

10 % KOH 




5 % HCl 





The free carbohydrate of the egg-white has also received a great 
amount of attention from an early date. In 1846 Winckler isolated 
a quantity of a sugar (4 grains) from the egg-white of the hen's egg, 
and identified it as lactose. ''Physiologists", he said, "will be able 
to tell me whether this is of importance for the embryo or whether 
it was some abnormality." The observation has not since been re- 
peated, and it is in the highest degree unlikely that any lactose was 
ever in an egg, unless the diet of the hen was a very unusual one. 
Budge and Aldridge soon were at work on this subject, the former 
concluding that the carbohydrate was glucose, but suggesting that 
it might form a disaccharide during development, and the latter 
making no concession to Winckler. The presence of glucose was 
afterwards abundantly established by the work of Barreswil ; Leh- 
mann ; Meissner ; Salkovski ; and Pavy. Later many quantitative 
estimations were made, and these are collected together in Table 16. 
The older figures for free carbohydrate may be regarded as fairly 








• ?^ 



































5 o 


*- 1^ bo 

iS S 


;- bD 
■ bo 



^ o bO 

1 c 


O 8 


I I 

I I 

in N I 
CO f^ 

coco I I I I I 

^ I U-)Co 

CO Lo « >ti 

CO I CO O ■-" 

05 CO t\ o) 

►1 ' M Cr^ C4 

CO OsCTi I «- O CO I 
I^ CT) IT) CO "J^ 04 

in o 



> rt g 

G u 
O O 










bo bo 

y bO 
I) w 

o o o o o o o 

O f< Crv o, JN, ^ Cl 
C< i~i -"i -^ --i IN >^ 


o <o Cr^l^ 

s « 

s 5 



« S P 

^ S; i>H '^ .^3 ^ ^ ti. g '^ tts tt, O O CO 

" -^ "^ "^ « s . ^ 

O G ^ 

Oh ? £ 



i~ iS it- V- 









C „ O u fi „ 
o - O 3 W " 

"bO bo 



six IN O O5 tx"5 

•S'S § 3 

o o ,0 ,0 ,0 00 o 

U "^ -« s ^ 

? 3 3 eg 

« ,a,» K c a 

S S ^55 ^ CJJ CJ Cj 

Ci u 55 1^ [^ tc, fcc, -^ cq Q, 





>*i •-< 


S2 3 • 

: C5 


■2 ?<> : 



C 3i 






•^ 0^ 



• 2 



^ a -<a. 




§ ■'2 






^ ^ 

■« a « 










trustworthy, but not for combined sugar, in view of the demonstra- 
tion of Holden that all copper-reducing methods are seriously inter- 
fered with by the presence of amino-acids and protein breakdown 
products. No method at present in use gives satisfactory results in 
those conditions, but the most reliable is that of Hagedorn & 
Jensen. No estimations of total carbohydrate in egg-white alone at 
present exist, but there is a single figure for glycogen due to Sakuragi. 
Morner found no evidence of fructose, pentoses or maltose. 

A curious phenomenon : the fluorescence of egg-white has been 
reported by van Waegeningh & Heesterman, but it only occurs if 
the egg is not perfectly fresh, and is therefore probably not physio- 

I '7. The Avian Yolk 

The vitelline membrane was investigated by Liebermann in il 
who found that it consisted almost exclusively of keratin. This he 
purified, and, having freed it from ash, made an elementary analysis 
of it, which is shown in Table loa. Some experiments which demon- 
strate the peculiarities of the vitelline membrane have been devised 
by Osborne & Kincaid. They found that a fresh yolk floated into 
distilled water, o-g per cent. NaCl solution, or glycerol, behaved 
exactly like a red blood corpuscle in that it swelled up and burst 
in the former, and shrank to a corrugated globe in the latter, while 
in the isotonic salt solution it remained unchanged. But with other 
treatment, nothing took place which corresponded to haemolysis. If 
the yolk was put into lo per cent. NaCl solution, it did not shrink, 
as had been expected, but swelled up, owing to the penetration of 
the saline and the consequent osmotic pressure due to the dissolving 
of the vitellin in the saline. This showed at once the scleroprotein 
nature of the membrane and its impermeability to vitellin even when 
in solution. The membrane is also impermeable to phosphatides and 
fats dissolved in ether, for if a yolk is put into ether it sinks and swells, 
so that the upper pole is distended by an accumulation of deeply 
pigmented ether. But until the yolk bursts, as it eventually does, 
not a trace of pigment or other substance passes out into the ether, 
and the same results were found with chloroform and carbon disul- 
phide. In alcohol, on the other hand, there is no swelling, for the 
alcoholic solution of phosphatides and other bodies can pass out 


through the keratin membrane. It would be very interesting to make 
a more extended study of the osmotic properties of the vitelline 
membrane (see in this connection Section 5*6). 

The yolk of the egg was investigated earlier in the modern period 
than the white. We may pass directly, excluding the curious analysis 
of the eggs of Struthio casuarius by Holger in 1822, to the papers of 
Gobley, which appeared from 1846 to 1850, and which, with those 
of Valenciennes & Fremy from 1854 to 1856, still remain models 
of embryo-chemical work. "John, a German chemist," said Gobley, 
"appears to have been the first to occupy himself with serious 
researches on the yolk of the egg. The chemists who preceded him 
considered it as made up only of water, albumen, oil, gelatine, and 
colouring matter; such was the opinion of Macquer, Fourcroy, and 
Thomson. John concluded from his experiments, which he published 
in 181 1, that the yolk was composed of water, a sweet yellow oil, 
traces of a free acid which he thought was phosphoric acid, and a 
small amount of a brownish red substance, soluble in ether and 
alcohol. Besides these he found gelatine, sulphur, and a great deal 
of a modified albuminous substance." Gobley referred also to the 
work of Prout, of Chevreul, of Berzelius and of Lecanu, who dis- 
covered the presence of cholesterol in yolk in 1829. 

Gobley himself found in the yolk nearly all the substances which 
we now know to be there. His own list of them ran as follows : 

1 . Water. 

2. An albuminous matter, "vitellin", 

3. Olein. 

4. Margarin. 

5. Cholesterin. 

6. Margaric acid. 

7. Oleic acid. 

8. Phosphoglycerilic acid. 

9. Lactic acid. 

10. Salts such as chloride of sodium, chloride of potassium, chlorhydrate 

of ammonium, sulphate of potash, phosphate of lime, and phos- 
phate of magnesia. 

11. A yellow colouring matter and a red colouring matter. 

12. An organic substance containing nitrogen, but which is not al- 


Most of the constituents of egg-yolk may be recognised under this 






V se 

9 3't= 

Z bo 





V a 

►S '-° 

-G „ 

i^g^l J35 2 5 w 

C^ ^^ O Ph ^ Ph C/D 1-1 

0~i c 
" — o 

s ^ 


1 •: 1 1 1 1 1 




a> CO lo CO oi 

1 1 M 1^ C4 O - 

1 ' io 'i' LO(-b io 



O S"! S? 

L4 U U 

c 3r, 

CO CO coco CO 
6 6 « 6 6 

CO O CO CO -^ ^ 
C< C< C< C4 W CO 

O O " 

M Oco lO" 01 coc<co cox> a in 
CO ■^ ^cb c) M M ciiT) ■^ CO CO CO 

O O yD CI C( 



eg 1^ 


0-2 '^ - 

"Phco " " 

^ 0-7^T3 « 


m lo^d t^ lO lO'Xi t^ t^t^ t^ t^to ^ 

o >p 

01 ►H 

r^ « O ^ 

M CTi CO lOCO f^ 

« 6 COti> 131 " 

CO CO CO CO c< c< 

w O 

CD lO CO ^ 
lO lo in t^ 

o CO a> Ti-co lo CO ■* Tj- CO o 

O ■* 1^ CO r^cp LOCO ^ CO t^ ^ ■^co r^ 7 

M^r^OCOi-CTiLO rhcb CTi f^ f^ f^ CT) -> 


o O 

'-30331'iU -^aj 

QOhOKffi K 

O « 
. C 

> y 


CO " O O lO 
lO CT) en lO C"! 

6 6 ci 6 io 

N " " c< " 

« „' en 

O « ^ « 


o E ~'-- 

X^ - 


o f^ 

u ^— ' 




1/3 o 

c ^ 
c _ 

CO 7*" r^ O 

1X> ^ C5 CT) 

CO ^ O K) 

6 6 « 6 

in ■* irs jj 

o in o 


(i ti t£i 

O) 6 Cl CD 
^ uO Tf ■* 


o o o o 

O -1 O CD 

(i> f^cb f^ 

lO lO lO lO 





* * 

K K^S 

bog g 

C C u O fc^ ^^ aj 

i3t)cubDl'-3 a 



be 3 u 


2 K 



E ^ 


2 -S 



old-fashioned terminology. Gobley made many quantitative observa- 
tions on the various substances, and his figures are given in Table 17, 
which sums up all the analyses that have been made of the yolk 
in the eggs of birds. The original discovery of vitellin was made by 
Dumas & Cahours, but Gobley was the first to make an extended 
study of it. His elementary analysis is given in Table 10 a. He knew 
that it contained both sulphur and phosphorus. Gobley was able to 
isolate oleic and margaric (palmitic) acids from the fat fraction of 
the yolk, but, unlike Planche twenty-five years before, he got no 
stearic, and Kodweiss, one year later, reported its presence under 
the impression that it had not been found before. Gobley, however, 
was easily able to repeat Lecanu's discovery of the presence of 
cholesterol, and made a remarkable examination of the lipoids. 
"These viscous materials", he said, "appear to have been considered 
by John as not being of a fatty nature at all. They form the most 
interesting part of the yolk; they contain all the phosphorus which 
exists there in considerable quantity." He analysed the glycero- 
phosphoric acid which he obtained from the lipoid, which he named 
"lecithin", and speculated as to the significance which it might have 
for the growth of the embryo. He also recognised that fatty acids 
and nitrogen were present in the viscous matter. 

Ten years later Valenciennes & Fremy made a further examina- 
tion of the yolks of a large variety of eggs with special reference to 
\itellin. It was they who discovered substances very similar to vitellin 
in the eggs of reptiles and fishes; these they named the ichthulins. 
As regards the eggs of birds, they contented themselves with con- 
firming the results of the previous in\'estigators, but they regarded 
vitellin as having practically the same constitution as fibrin, on the 
grounds of elementary composition only. At the same time, they held 
it to be a different compound because it would not, like blood fibrin, 
decompose hydrogen peroxide. 

If Table 1 7 is examined, it will be seen that the yolk is much drier 
than the white in all birds' eggs examined, having only about 50 per 
cent, of water as against the 85 per cent, of the latter. On the other 
hand, the percentage of fatty substances and lipoids is much higher, 
being just about double the amount of protein, whether related to 
wet weight or to dry. It is noticeable from the analyses of Tarchanov 
that the yolks of eggs from nidicolous birds having a short incubation 
time are about 10 per cent, richer in water than yolks from the eggs 


of nidifugous birds. This must imply that the greater requirement 
for nutrient material in the latter case has, as it were, packed the 
fat tighter into the yolk. Exactly the same relationship is brought 
out from the figures of Spohn & Riddle, who compared the pigeon 
which hatches out as a squab with the hen which hatches out as a 
fully-feathered chick. Spohn & Riddle's analyses are the only com- 
plete ones we have for a nidicolous egg, and bear clearly the same 
relationship, for there is less protein and less fat, relatively, in the 
pigeon's egg than in the hen's. The ash content and the amount of 
non-nitrogenous extractive substances seem, however, to be slightly 
higher in the latter case. Langworthy's figures were all obtained 
from the eggs of nidifugous birds, and they show a great similarity 
among themselves. More delicate consideration, of course, reveals 
differences according to breed in the hen's egg, e.g. the figures of 
Pennington and his collaborators, but these are of a comparatively 
minor order. 

The most interesting analyses are those of Spohn & Riddle. They 
compared the egg of the jungle-fowl, which is supposed to have been 
the evolutionary ancestor of the domestic hen, with averaged figures 
for hen's eggs of various breeds, and, as is evident, there was a very 
close agreement. They also analysed the white yolk as distinct from 
the yellow yolk of the hen's tgg. When the yolk begins to be formed 
in the ovary of the hen, it is white and not yellow, and not until 
the critical point in its maturation is reached, when its growth-rate 
completely changes, does it begin to store lipochrome pigment. This 
change in growth-rate, which has been observed by other workers 
as well as Riddle (e.g. Walton), will be dealt with in more detail 
in the appendix on maturation. Von Hemsbach, in a paper on the 
milky or white yolk of the birds, in 1851, suggested that the corpus 
luteum of mammals corresponded to the yellow yolk of birds, and 
that the mammalian ovum having been shed out of the ovary into 
the Fallopian tube and uterus, the fats and lipochrome pigment 
were laid down in the Graafian follicle instead of around the white 
*'ovum". Von Hemsbach also supported the view already mentioned 
that the shells of avian and amphibian eggs corresponded to the 
decidua of mammals. He laid stress on the work of Zwicky and 
Gobel, who had investigated the pigments of yolk and corpus luteum, 
and had thought them to be identical. This subject will be referred 
to again under the head of pigments. 




In the fresh egg, as laid, the white yolk occupies a central position, 
and is surrounded by concentric layers of yellow yolk. But as a kind 
of cylindrical prolongation of the white yolk reaches to the surface 
of the vitellus underneath the blastodisc or germinal spot, the white 
yolk must be considered the first food of the embryo, and, until its 
composition was determined, it was not possible to say what sort 
of nutrient environment the embryo possessed in the very early days 
of development, although the composition of the yellow yolk would 
give this for the later period. The histological differences between 
white and yellow yolk had been known for a long time (see Purkinje ; 
His ; Leuckart ; Klebs ; Dursy ; Strieker ; and Virchow) but Riddle 
and Spohn & Riddle were the first to approach the subject chemically. 
Their figures showed that the white yolk much the more nearly 
approximated to the contents of invertebrate eggs with holoblastic 
cleavage, and living undifferentiated tissue generally. Instead of 45 per 
cent, of water, the white yolk had 86 per cent., instead of 15 per cent, 
of protein, it had only 4, and instead of 25 per cent, of fat it had 
only 2. Thus in its water-content, it was much more like {a) egg- 
white and {b) the young embryo itself than like ordinary yolk, while 
instead of having twice as much fat as protein it had twice as much 
protein as fat. These data are extremely interesting in view of the 
facts that are known about the sources of energy made use of by the 
embryo during its development. Although by far the greatest pro- 
portion by weight of substance combusted during embryonic life is 
fat, yet, in the early stages, the embryo undoubtedly gets its energy 
preponderantly from protein and carbohydrate (see the whole of 
Section 7). The percentage of non-nitrogenous extractives did not 
differ much between white and yellow yolk in the experiments of 
Spohn & Riddle, but it would be very interesting to know the 
relative amounts of carbohydrate, and analyses to discover this should 
certainly be done. Again, the yellow yolk contained eight times less ash 
than the white yolk, a finding which acquires considerable significance 
from the fact that, if the ratio inorganic substance/organic substance 
in the embryonic body is plotted, it is seen to descend steadily 
from the beginning of development (see Fig. 249). Moreover, as 
Mendeleef has shown, early embryonic cells contain twice as much 
electrolyte as those of later stages (see Section 5"8). The amount of 
phosphatide in the yellow yolk, furthermore, was ten times that in 
the white, a significant difference; for, as Plimmer & Scott have shown, 


one of the main functions of the phosphatide is in furnishing phos- 
phorus for the embryonic bones during the period of ossification, a 
requirement which is not present in the earher stages of the develop- 
ment. The histochemical work of Marza, who compared the white 
and yellow yolk following the method of Romieu, is in agreement 
with this, for he found the elements of the yellow yolk to be richer 
than those of the white. (See Plate X.) 

1-8. The Avian Yolk-proteins 

As regards the protein, vitellin (Tables 10 a and 11), several interest- 
ing points are to be observed. The best elementary analyses of ovo- 
vitellin are probably those of Osborne & Campbell. After its discovery 
by Dumas & Cahours, Gobley, and Valenciennes & Fremy, it was 
studied by Hoppe-Seyler, and now for the first time with special refer- 
ence to its position in the classification of the proteins. Virchow had some 
time before then suggested that the yolk-platelets, familiar to histolo- 
gists, contained lecithin, and there had been some doubt as to their 
nature. Valenciennes & Fremy had opposed the view that they were 
crystals, basing their view on Sennarmont's work, but Radlkofer and 
Hoppe-Seyler returned to the crystal theory. Hoppe-Seyler believed 
that vitellin contained no phosphorus, but that what appeared in the 
analyses was due to contamination with lecithin. This view was sup- 
ported also by his assistant, Diakonov, who contributed to the Med.Chem. 
Untersuchungen one of the earliest investigations of phosphatide. But at 
the same time Miescher obtained from the yolk of the hen's egg a sub- 
stance containing a great deal of phosphorus, and possessing certain 
of the properties of a protein. This he believed to be nuclein. "It is 
interesting ", he said, "in relation to the origin of nuclear substance, 
that the nutrient yolk contains ready-formed nuclein in significant 
quantity." At this time, then, the proteins of the yolk were believed 
to be ovoglobulin (for so Hoppe-Seyler called the vitellin of the 
earlier workers) and Miescher's nuclein. Miescher himself identified 
his nuclein as a constituent of the white yolk of the histologists, but 
he noted that the hen's egg seemed to have no xanthine in it. 

Lehmann, Schwarzenbach and others, however, did not agree with 
this classification, and regarded vitellin as a mixture of albumen 
and casein. They did so not on the grounds of its containing phos- 
phorus, but because they found that rennin would completely 
coagulate it from its pure solution. But this attitude did not prevail. 


and the word " nucleovitellin " became general, until Kossel in 1886 
found that, if vitellin was really a nuclein, it differed from all other 
such substances by giving no trace of xanthine after acid hydrolysis. 
On the other hand, true nuclein, he found, was present by the tenth 
day of development. Hall and Burian & Schur, Bessau and von 
Fellenberg confirmed this absence of purines from the fresh egg. In 
more recent times, Sendju and Mendel & Leavenworth have found 
exceedingly small amounts of true nucleoprotein (2 and i*6 mgm. 
per cent, respectively wet weight) in the hen's egg (by purine bases), 
and Plimmer & Scott, and Heubner & Reeb have done the same (by 
phosphorus analysis) . Shortly after Kossel's work, Milroy found that 
vitellin gave a biuret test though no Millon, and materially differed 
in nitrogen and phosphorus content from any of the nucleoproteins, 
while, at the same time, Miescher admitted that he could not isolate 
any purine bases from his "nuclein" in the hen's egg. Levene 
& Alsberg next investigated the manner of breakdown of vitellin, 
finding the substance they named " paranuclein " after digestion with 
pepsin, and "avivitellic acid" after hydrolysing with ammonia. The 
elementary composition of these substances is given in Table 10 a, 
from which it could be seen that the increasing phosphorus content 
implied the presence of phosphorus as an important constituent of 
the original molecule. Six years later Levene & Alsberg ascertained 
the amino-acid distribution (see Table 11). They pointed out the 
significance of the high proline figure, in view of the task of haemo- 
globin synthesis which the young embryo has before it. Abderhalden 
& Hunter and Hugounenq undertook a like investigation in the same 
year, from which a striking similarity between the amino-acid dis- 
tribution in vitellin and casein came to light, especially as regards 
the high proportion of leucine and glutamic acid. They drew atten- 
tion to the similarity in physiological requirements as between the 
"erste Nahrung" of chick and mammal. The historical associations 
of this discovery have already been referred to (see p. 53). It was 
at this time that Neuberg, and Blumenthal & Mayer reported the 
existence of glucosamine in the vitellin molecule, two observations 
which stood together in isolation, until in 1929 Levene & Mori 
isolated from egg-yolk the same trisaccharide which they found to 
be present in ovoalbumen and ovomucoid and which has been re- 
ferred to above. 

It was not until the paper of Bayliss & Plimmer in 1906 that the 



/ kj^EHHHH^^^HHI 

' '^ " 


Stain, haemalum-eosin: magnification, gxA: prepared and microphotographed by 
Dr V. Marza. The stratification of the yolk into white and yellow is beginning. 


nature of vitellin really became clear. They subjected casein 
and vitellin to the action of trypsin, and studied the time taken under 
varying conditions for the phosphorus to be split off into soluble 
form. Ovovitellin, they found, was much more slowly digested than 
casein, for after 36 days only half of its phosphorus had been made 
soluble, whereas after 2 or 3 days a large percentage of the casein 
phosphorus had gone into solution in inorganic form, and most of 
the rest was present in water-soluble organic combination, i per 
cent, soda, however, would bring aU the phosphorus of casein into 
solution in 24 hours. BayUss & Plimmer concluded that ovovitellin 
and casein were both phosphoproteins, as distinguished from nucleo- 
protein, where the phosphorus would be present in the prosthetic 
group and not in the protein itself Plimmer & Scott later found that 
ovovitellin behaved in the same way to soda. This reaction served 
to distinguish between phosphoproteins and nucleoproteins, for all 
the latter, it was found, were stable to alkali and easily split by 
acids. From the phosphorus distribution in the unincubated hen's 
egg, Plimmer & Scott concluded that vitelHn accounted for at 
least 30 per cent, of the phosphorus, and this led them on to their 
investigation of the changes which take place in the different 
phosphorus fractions during the development of the embryo. 

The distribution of phosphorus-containing compounds in egg-yolk, 
as Plimmer & Scott found, makes a very different picture from that of 
any other tissue. Their summary is shown in the accompanying table 
(18). It would be extremely interesting to investigate the phosphorus 
distribution in the white yolk, which at present is altogether uncharted. 

Table 18. Phosphorus in per cent, of the total phosphorus. 









Lecithin P ... 





Total water-soluble P 





Water-soluble inorganic P 





Nucleoprotein P 





Phosphoprotein P ... 





Total protein P 





The third of these fractions i 

includes the phosph 

orus of all unstable water-soluble corn- 


Steudel, Ellinghaus & Gottschalk have recently found that vitellin 
behaves towards pepsin exactly like casein. The rate of increase of 
titratable COOH groups during the digestion far exceeds that of 
NH2 groups, reaching a maximum about the fourth hour. The 




[PT. Ill 

Table 19. 

Per cent, of dry weight 

Total N 



N/P rati 

mer's figures. 

Ovovitellin ... 
ovolivetin ... 
Ovoalbumen ... 
Casein ... 

... 15-29 

••• 15-51 
... 15-30 





Levene & Alsberg's figures. 

Avivitellic acid ... 13-13 

Swigel & Posternak's figures. 


Swigel & Posternak's figures. 

Hydrolysis of ovotyrine b^ (% ) 
H3PO4 acid NH3 Arginine Histidine Lysine 

12-00 1-60 4-90 0-62 0-70 0-75 


Ovotyrine a^ ... 

... 10-87 




Ovotyrine ^^ ... 

... 11-33 




Ovotyrine /Sj ... 

... 10-92 




Ovotyrine 71 ... 






Table 20. Nitrogen distribution. 

Plimmer's figures (1908). 

Per cent of dry weight 


Ovovitellin . 
Ovolivetin . 













amino N 

linkages must break, therefore, between a carboxyl group and pro- 
line, tr-yptophane, histidine or arginine. 

Weyl ; v. Moraczevski ; and Gross were the first to describe the 
properties of the egg-yolk proteins, but the standard account is that 
of Plimmer, who in 1908 identified two yolk-proteins, ovovitellin, 
and ovolivetin. Ovovitellin, according to his analyses, contained 
1*0 per cent, of phosphorus, but ovolivetin only o-i per cent. He was 
usually able to isolate far more of the former than the latter, but in 
some experiments the yield seemed to be nearly equal. Livetin was 

SECT. l] 



soluble in water as well as 10 per cent, salt solution, but it cannot be 
ovoalbumen or any of the egg-white proteins, for it is not coagulated 
by ether. Plimmer suggested that possibly livetin was vitellin with 
the majority of the phosphorus-containing parts split off from it. 
Tables 19, 20 contain Plimmer's figures for these two proteins. 

Table 21. 


May & Rose 

Folin & Looney 

(1922), (%) 

(1922), (%) 






















Free tryptophane (% of whole egg) 

von Fiirth 

& Lieben 

Ide (1921) 


Whole egg-contents 








"otal tryptophane. 

(% of proteins) 

(% of proteins) 

Whole egg-contents 









Whole egg-contents 



Ovovitellin has been the subject of recent investigations by Swigel 
& Posternak. They found that it broke up into three polypeptides 
which they call ovotyrine a^, ^^ and y^. The properties of these are 
listed in Table 19. It was found that ovotyrine ^ contained all the 
iron in the original compound, and that it could be split up into 
ovotyrine /Sj and ovotyrine ^2 the second of which again contained 
all the iron. All these derivatives were laevorotatory, and showed 
considerable resemblance to the lactotyrines which the same workers 
had previously isolated from casein. They identified their ovotyrine ^ 
with the avivitellic acid of Levene & Alsberg, and they stated that 
an enzyme was present in the fresh yolk which would, on standing 
at 37° C. for 10 days, double the yield of preformed ovotyrine jS. 


— - u 

O 3 

5P =0 § a 







•ft IN 



orjouii % I 

XxojpAq % I 

DUBajs % I 

oijnuiBd % I 

oiajo % O 


oijAjnq % I 

3% I 

N% I 

•3 -ds I 

xspui aApoBija^j | 
•ou jauqaH ^^ 

•ou ]A}30V I 


anjBA jajsg r~ 


an^BA ppv ? 


I I 

in CO 

O) o 



•ou auipoj 

coco o -^ p eo^ oj w Tho^eoco 
Tt< e« fj " a f^ ^ii> N tJ< 6 f^ o» 
'X> (^ t^co lo cotn i^co r^ c< <J) lO 

in o coco 
(ij 6 CO 6 
CO t^UD i^ 

::::::: c 

fl S^ ci o o 

< -C(V C^tH in 

•3 "^ u . "^ <« ?4 

^ D o5i ° n£,-£. 

iH Pffiffi 

2 2^ &• ^ 


g jj o s;a cn 

c c fi 2 c 2 3 



^ « « ^ a 

^ o o 

'^ - - •< « 




CO J2 

s i 


3 S3 w 


v5 «^ 

s >- p fl 

pHC/2y3 3H 















O f~~ CO mCO CT) ^ ■*C0 iD 

CT:cb w c< 6 '^ •4'6d ^ CO 
(£1 •*co r^ r^to i~~ i^ CO (j2 


^ bo "^ 

.ii.a a i^z 

c« oj y u c &. c 

^ ci, u X! :r! u=! *■ 

a c c c c c V 

o o o o o o 


g C3 g 

c £ « •- 

o V o a 

"* c e 

o o 




Hydrolysis of ovotyrine ^ revealed the presence of large amounts 
of /-serine, an amino-acid which had not previously been found in 
ovovitellin (see e.g. Plimmer & Rosedale's analyses). Some pyruvic 
acid and ammonia being given off as well, Swigel & Posternak 
calculated that, supposing these arose from breakdown of serine, 
there would have been sufficient serine present initially to combine 
with for all the phosphorus. They therefore suggested that the main 
phosphorus-containing unit of ovovitellin was serine-phosphoric acid. 

Cohn, Hendry & Prentiss consider the minimal molecular weight 
of vitellin to be 192,000, i.e. much higher than ovoalbumen. 

Kay & Marshall have also studied the yolk-proteins. They have 
prepared purer samples of vitellin and livetin than those of any 
previous worker, and have been able to free the former almost 
entirely from contamination with ovolecithin. Their vitellin is a true 
phosphoprotein containing i -3 per cent, of phosphorus and hydrolysed 
by I per cent, soda, though not by the phosphatase of the kidney. 
Their livetin is a pseudo-globulin, containing only the slightest 
traces of phosphorus (less than 0-05 per cent.). The yolk of the 
fresh egg contains no albumen. Vitellin, hydrolysed with dilute 
ammonia, gives a vitellinic acid containing about 10 per cent, of 
phosphorus. Kay has estimated the cystine, tryptophane and tyrosine 
in vitellin and livetin (Table 11); in the latter protein they are dis- 
tinctly high in amount, a fact of some importance in embryonic 
nutrition. The relative amounts of vitellin and livetin in yolk would 
appear to be of the order of 3-6 to i for the hen and 3-8 to i for the 
duck, calculating from their nitrogen content. Kay regards livetin 
as identical with Gross' protein. The yolk of a fresh egg would 
contain from 600 to 900 mgm. 

1*9. The Fat and Carbohydrate of Avian Yolk 

The fatty acids of the yolk have been much investigated since the 
time of Gobley and Kodweiss, but little has been added to our know- 
ledge of them. Paladino found olein, palmitin and stearin to be 
present. Analytical details are in Table 22. 

A large part of the study of phosphatides, under the generic name 
of lecithin, has been made on that obtained from the yolk of the egg; 
thus the work of Diaconov, who showed it contained no neurine, 
Strecker, who discovered the presence of choline, Bergell ; Cousin ; 
Laves & Grohmann; Laves; Wintgen & Keller; Erlandsen; Stern 


& Thierfelder; Frankel & Bolaffio (whose egg-yolk neottin was only 
a mixture of sphingomyelin and cerebrosides), McLean; Serono & 
Palozzi; Eppler; Riedel; Wilson, and Trier, who prepared amino- 
ethylalcohol from it, all comes under this heading. In McLean's 
book will be found a review of it. Certain aspects of it, however, are 
important here ; for instance, the question of the presence of very 
unsaturated acids in ovolecithin. McLean in 1909 found stearic and 
oleic acids in it, but Cousin was able to isolate linolenic and palmitic 
as well, and Riedel; Hatakeyama; and Levene & Rolf obtained 
linolic and arachidonic acids. In another paper Levene & Rolf 
showed that the lecithin, carefully freed from kephalin, contained 
only palmitic, stearic, and oleic acids : saturated and unsaturated 
molecules being present in equal proportions. Again, Stephenson in 
1 9 1 2 found an acid in the phosphatide fraction from egg-yolk, which 
had 20 carbon atoms and 6 or 8 unsaturated linkages. Although 
the proportion of unsaturated acids in egg-yolk is generally agreed 
to be small, yet it may be of importance for the young embryo if 
it passes through a period in the early developmental stages before 
it has the power of desaturating the ordinary fatty acids. Evidence 
which suggests this will be presented later (Section 1 1 • i ) . 

The nitrogenous radicle in ovolecithin is largely choline, but 
difficulty was at first experienced in obtaining a theoretical yield 
on hydrolysis; thus Moruzzi got only 77 per cent, in 1908 and 
McLean only 65 per cent, in 1909. This was accounted for, however, 
when it was found that amino-ethyl alcohol was also present. The 
two bases together make up all the nitrogen in the molecule. Erlandsen 
was the first to question the view that lecithin alone accounted for 
the phosphatide fraction, but he was not himself able to isolate any- 
thing else. Later workers (Levene & West and Stern & Thierfelder), 
however, found that kephalin is also present in yolk, and it would 
probably be in the kephalin molecule that the unsaturated fatty acids 
would be present. Analyses of kephalin from the yolks of fowls are 
given in Table 10 ^. McLean in 1909 isolated from egg-yolk a third 
phosphatide which resembled cuorin, but it is very doubtful whether 
this was a true chemical individual. Sphingomyelin has also been 
found in egg-yolk by Levene (191 6), and lignoceric as well as hydroxy- 
stearic acid was present in it. 

All these substances exist in the yolk in close association with 
the proteins. Hoppe-Seyler it was who first observed that, after 


prolonged extraction of the yolk with ether, a considerable proportion 
of the phosphatides still remained behind, and could be extracted 
with alcohol. It was thought for a long time that the phosphatides 
and the vitellin were in chemical combination which was broken 
by the alcohol, but since the paper of Fischer & Hooker in 1 9 1 6 the 
general opinion has been that this combination is only physical. 
Stern & Thierfelder isolated traces of the cerebrosides, phrenosin and 
kerasin, from egg-yolk in 1907. 

The neutral fats and the lipoids of the yolk are variously affected 
by the nature of the fats in the food of the fowl. Henriques & Hansen, 
who were the first to investigate this subject, found that, if food con- 
taining very unsaturated acids was fed to the laying hens, the neutral 
fats in the eggs were affected, but not the fatty acid components of 
the lecithin. Their figures are shown in Table 22. When the food 
consisted of barley, pea or rice, the iodine number of the neutral 
fats in the egg varied round about 77, but hemp or linseed sent it 
up to about no, although no matter what the food was the iodine 
number of the fatty acids in the phosphatide fraction remained con- 
stant at 75 or so. Henriques & Hansen also found that the iodine 
number of the fluid fatty acids of the neutral fat was normally 107-5, 
and that the fluid and solid fatty acids of the phosphatide fraction 
were 151-3 and 98-9 respectively. The former accounted for 64-3 per 
cent, of the lecithin fatty acids. The experiments of Henriques & 
Hansen have been repeated and confirmed by Belin and by Terroine 
& Belin. The last-named workers, together with McCollum, Halpin 
& Drescher, some years later reported that the lecithin fatty acids 
would vary, as well as the neutral fatty acids, with the diet of the 
hen. Their figures, which are given in Table 22, certainly show a 
variation in the iodine numbers of both fractions. All these workers 
recognised the presence of unsaturated acids in the yolk fat, and 
Henriques and Hansen's figures came between the theoretical values 
for oleic and linolic acids. 

Work was continued along these lines by McGlure & Carr. Using 
pigeons, they found that the fat content of the eggs could only be 
altered slightly by feeding rations high and low in fat. 

% fat in the eggs 
Cocoanut fat ... ... ... 4-0 

Beef tallow ... ... ... ... 6-75 

Average of all fat diets ... ... 4-96 

Average of all non-fat diets ... 4-81 


■^ ^ 


be ffi 


















C5 •: 


(U bO S 

{ij OUIUIE 33JJ 

^ OUIUIB l^jox 

^ uiajojd 

Ivj UI3JOjd-UOU 


|«j^ upjojd 

N F50X 


^ ouiuiB aaaj 

^ UT3}Ojd 

^ uiajojd 

fvj OUIUIE 331^ 

fy[ asouinqiY 



\[ uiajojd 

I^J upjojd-uou 

|vj uiajojd 



bo !^ 

•j3 "O 










tr, u:, 





!r> o 


o o o 

O ^ IN 
ir^ lO 1^^ 

OO ir>OoO,oOO 
COtXJ ,O^0D IT) O <0 LO CO 

' « «" <N «'" -^ kT ;^ «" cT 




V • 

^ s 

bo w 

• O 

e & 

be V 

S I: 

"O S 
c « 

o >^ 



Si 3 

o ^o 

«j be 

^ s 



p « 
CO 3 


^ «^, CO 

^ r/1 S S be O 
-S^-S «J bco 




o 5 3S S ^>^ ^-^ S^.^ 


^ g § ^ 



[PT. Ill 

Again, during the fat feeding, tiie saponification value of the egg- 
fat was 176 (166-190) and during the rest of the time 173. The iodine 
value was in the former case 70-5 and in the latter 70-8. 

Table 24. Lipoid in egg-yolk. 




/o /o 
Wet weight Dry weight 
























Glikin' s figures. 


P,05 in Lecithin 




% of in % 



% dry 

fatty of fatty 




acids acids 


Pigeon (yolk) 



3- 16 35-73 




3-88 38-42 


Turtledove (yolk) 



4-10 46-65 


Starling (whole egg) ... 


5-67 64-44 


Hen (yolk) 



— — 


Cat ... 

Lecithin in % dry 
weight at birth or hatching 

Some suggestive investigations on the biological significance of 
ovolecithin were made b-y Glikin in 1 908, whose figures are shown in 
Table 24. Choosing the pigeon as a typically nidicolous bird, and 
the hen as a typically nidifugous one, he was able to show, using a 
variety of extraction methods, that the yolk of the former was con- 
siderably richer in lecithin than the latter, the former containing 
about 29 per cent, dry weight, and the latter about 17. The further 
but rather fragmentary observations which he made on the starling 
and the turtledove confirmed this relationship. It is interesting that 
Tso informs us that certain small Chinese breeds of hen produce very 
small eggs (scarcely 40 gm.) and that these contain a much higher per- 
centage of lipoids than ordinary eggs though an equivalent percentage 
of protein. He concluded that lecithin, one of the most essential 
yolk-constituents, was specially concentrated in nidicolous yolks and 


was associated with the property of early hatching or birth. Thus 
he compared the thrush (nidicolous) with the guinea-pig, which is 
born almost ready to eat green food and hardly passes through a 
lactation stage; in the body of the former 8 gm. per cent, lecithin dry 
weight was found, in the latter only 4. The new-born cat and rabbit 
occupied intermediate positions. It is interesting to note that Glikin's 
figures bear out those of Tarchanov on the question of water-content 
of yolks from the two types of birds. 

Tornani affirmed in 1909 that a difference in lecithin-content was 
observable between fertilised and unfertilised eggs. But as he gave 
no figures in support of his contention, it has not been treated with 
much respect by subsequent workers. 

The carbohydrate of the yolk has been the subject of only a very 
few researches compared with that of the white. The figures which 
have been obtained are shown in Table 16, and it will be seen that 
in no case has the total carbohydrate been estimated, and only 
in one case the glycogen. After Claude Bernard's isolation of gly- 
cogen from the yolk, a persistent belief grew up that considerable 
amounts of this substance were present there ; this was apparently 
based on the description by Dareste in 1879 of "amyloid bodies" in 
the yolk which gave microchemically a strong blue colour with 
iodine. Dastre immediately pointed out that the occurrence of starch 
there was highly improbable, and that if any glycogen was there it 
should give a wine-red colour; he himself, however, could find 
neither. But he did not succeed in suppressing the rumour, for 
Virchow, and later Schenk, supported Dareste, though nothing has 
been heard of this yolk-constituent since 1897, and Sakuragi's 
analysis revealed the presence of only 2-2 mgm. per cent, of glycogen. 
Bierry, Hazard & Ranc asserted in 191 2 that they could obtain a 
great increase of carbohydrate after hydrolysing the yolk with 
hydrofluoric acid under pressure, but this would not imply, as they 
seemed to think, that glycogen was present, for all kinds of other 
compounds such as proteins (Gross' protein for instance) might yield 
glucosamine under such treatment. They identified glucosamine in 
the hydrolysate. On the other hand, Diamare, who hydrolysed with 
acetic acid, could only obtain faint traces of combined glucose in 
the yolk. He dialysed both white and yolk, and in both cases was 
able to estimate the free sugar, but in the case of the yolk very little 
combined glucose seemed to be present. Further studies on this 


subject should be undertaken, for the methods of Diamare and Bierry 
ahke were of questionable reliability. Diamare, however, went rather 
further into the matter than other investigators, and, thinking that 
the yolk glucose might only be present there owing to an inflow from 
the white, examined the ovarian eggs, in which he found glucose in 
much the same proportion as in the yolks of laid eggs. He does not 
state whether the ovarian eggs were yellow or white, and, as he 
frequently gives his results in the form of grams of glucose without 
mentioning the weight of the fresh material, it is impossible to calcu- 
late the percentage (see also Tillmans & Philippi) . 

We have already seen that cholesterol was identified in the yolk 
of the hen's egg by very early workers such as Gobley. In 1908 
Menozzi and in 191 5 Berg & Angerhausen sho\ved that egg cholesterol 
was identical with that from milk and bile. It is certainly present 
in the unincubated yolk both free and in esterified form with fatty 
acids. Serono and Palozzi investigated a substance from egg-yolk in 
191 1 which they called "lutein" but which turned out to be nothing 
but a mixture of cholesterol esters. Other investigators have estimated 
the amount of free and combined cholesterol in the unincubated egg, 
and their figures are given in Table 25. 

Table 25. Cholesterol-content of hen^s egg. 


per whole egg 

Investigator and date 

Parke (1866) 

Mendel & Leavenworth (1908) 
Mueller (1915) ... 
Ellis & Gardner (1909)... 
Thannhauser & Schaber (1923) 

Cappenberg (1909) 

Dam (1929) 

Schonheimer (1929) 

Cholesterol Cholesterol 
(free) esters 

378 - 
215-9 24-2 
489 - 
173 54-2 

296 — 
337 — 



Free in % 
of total 





Many Other substances have been found to be present in the egg at the 
beginning of development, e.g. choline, alcohol, creatine, creatinine, 
inositogen, lactic acid, plasmalogen (Stepp, Feulgen & Voit, 1927), 
etc. These will be mentioned as occasion arises during the succeeding 
sections of the book. Allantoin is not present (Ackroyd). 

The yolk of the hen's egg also contains vitamines, pigments, and 
a variety of enzymes, but these will be dealt with under their respec- 
tive sections. As Langworthy has shown, it may also contain very 


? CO V C -!i; Ci cfl an 

S: o' " ?^M ^ ? 

o o>^ 


en M O 

C — O" 

5 2- 

e5 c9 fc, 

08 O'c 

<u Q 3 







•5 c 





fa es> 


E 0) 

s a " u 

-§ S f^a• 
0^^ ^ mi 

:ja :' 

"ego c 

>^4 :: 

d uispnjsj 

d aiqnios 


d ajqnios 
J aiqnios 

J upjojd 

d appEqdsoqj 

d unPMA 

d ajqnjos 


-J31BM 3UIe3jo So I 

d aiqnios "I 

-J31BM pjOX, g f 

d siqnps 
-loqooiB iBjox ^ 

(uonoB.ijxa ^ 
jaqja iajje) d r 

d aiqnios-jaqja | 



d aiqnps n 


d aiqnjos r 
-ja^BM 3jub3jo 

d aiqnios | 
-jajEM iBiox 

d siqnios 


(uotjoBjaxs 7^ 

jaqaa iajjE) d j^ 

ajqnjos-ioqoDiv ip 

d aiqnps-jsqjg ], 

d lElox 

t^ m >^ iri v^o O O 

O (U 

^ >. -• 

*^'o "u 


j: a 




(U u 
T3 « 

C O 
3 ^ 

5 ° 

•^ D. 

a 1 

m (U 

o c 

V C 

3 ao 

■+ir) 000 


Q X 



various substances derived from the diet of the hen, and these, if 
they are odorous or possess taste may very easily betray their presence 
(e.g. the Swedish "Schareneier" described by Hansson). Table 23 
gives the figures which are available for the nitrogen and Table 26 
for the phosphorus distribution. These summaries bear out on a 
detailed basis what has already been said. 

I -10. The Ash of the Avian Egg 

The ash of the yolk and the white of the hen's egg has been in- 
vestigated by several workers, and a study of it reveals certain inter- 
esting features. If Table 27 be examined, it will be seen that, in the 
yolk as well as the white, potassium has almost invariably been found 
to be present in greater amount than sodium. This is one of the 
characteristics of the egg-cell, as will be seen later when the eggs of 
other animals are considered. The yolk is also marked by the very 
high percentage of phosphorus, most of which is, in accordance with 
other evidence, in organic combination. The calcium is also mainly 
in the yolk, as is the iron, but not the magnesium. If now the amounts 
of metallic and acidic ion be calculated out in millimols and milli- 
equivalents per cent, wet weight, it is found that in both yolk and 
white there is an uneven balance, but while in the former case there 
is much more anion than cation (anion/cation ratio above unity), in 
the latter case the exact reverse holds, and the anion/cation ratio is 
somewhat below unity, about 0-55. In the white, therefore, some of 
the potassium and sodium must be combined with the proteins, as 
ovoalbumenates, etc.* However, the excess of cation over anion in 
the white is not so considerable as the excess of anion over cation 
in the yolk, and, bearing in mind also the much higher percentage 
of solid in the yolk than in the white, it would be expected that the 
anion/cation ratio of the whole egg would be greater than unity, 
and would approach that of the yolk. The facts show that this is, 
indeed, the case, for the average anion/cation ratio calculated from 
the results of all observers for the whole egg is 2-3, as against 2-8 
for the yolk alone and 0-54 for the white alone. This was first noted 
by Garpiaux. Forbes, Beegle & Mensching expressed it simply thus : 

Cubic centimetres normal solution 
per 1 00 gm. dry weight egg 
Total acid ... ... ... 120-28 

Total base ... ... ... 39*42 

Excess acid over base ... ... 8o'86 

* In both white and yolk, of course, the inorganic ash is basic. 

Hen ... 


Table 27. Aili of the avian 


% of total ash 








PO, c 








79-8 - 








79-1 — 








Bi-2 15-2 

Mgm./loo gm. wet weight 

K Na Mg Ca 

2-59 2-72 0-75 3-28 

)-33 048 0-79 3-5 

Fe SO, PO, 

.,.„. . , Total cation Total anion 

Millicquivalents . '■ ^ , * ^ Anion/ 

K Na Mg Ca Fe SO, PO. CI mols equiv. mob equiv. ratio Investigator and date 

3 — 2-59 2-72 1-50 6-56 — — 30-9 — 9-34 ,j.j7 ,0-3 jo-j 231 Polcck (1850) 

y - 3-33 0-48 1-58 7-u - - 35-7 - 8-t ,2-39 ,,-9 jj.7 ,.-88 Rose (1850) 

65 738 4-5 0-9. 1-66 7-0 — _ 34-95 7.38 9-79 /.,■„ ,9.03 ^.^j 3.00 Bialascewicz (1926) 

3-32 50-3 S'll" 173 204 

93 — 3-8 604 ]o8 443 8-8 0-34 

004 636 302 443 

4-6 — o-o8 19-08 

S-j/ 9-42 s2-;a 

Plimmer & Lowtidnt (1927) 
Vaughan & Bills (t878) 
Delezeime & Foumeau (1918) 

Carpiaux {1908) 
Buckner & Martin ( 


)125 17-5 273 fo 

)I30 15-4 23-8 Trace 

3-590 23-55 ao-7 0-96 

0-720 a7-tiG i'2-i 2-7 

0-634 — — 24-B 25 

o-Goo 22-1 20-63 1-41 I 

















0-52 2-9 1 








0-24 o-.e 

■ 2 



o-Bi 052 




0-65 0-40 

3-56 5-3 
5-11 3-8 









7-17 77-0^ 0-C25 Champion & Pellet (1876) 

(not very reliable) 
7-77 17-84 0-G29 


0-9 4-4 9-39 s-s8 

S-72 0-58 Poleck (1850) 

3-51 4-12 035 Rose(iB5o) 

- - - Voit(,877) 
4-82 ssf c-55 lljin (1917) 

— — — Prout (1822) 

— — — — 4-25' — 

523 4-l'8 3-79 1-24 8-72 - 
345 '0-9 '-"8 2-2 13-62 — 

129-a 52-5 

85-5 4-25 
Go- 16 3-6 
84-6 — 

64-7 1-8 
48-4 3-7 

.■58 6-6 
!-48 9-0 
2-4 9-6 


Average ... 0-54 


- - 139-8 

Straub & Hoogcrduyn (1929) 

Poleck (1850) 

Rose (1850) 

Voit (1877) 

Carpiaux (1903) 

lljin (1917) 

Prout (1822) 

Straub & Hoogerduyn (1929) 

*Kreis & Studinger. 


This is probably the most interesting consideration that emerges 
from Table 27, but it may also be noted that the ash-content of the 
white is just about half that of the yolk, a relation which would 
practically be reduced to equality if the phosphorus in the yolk was 
not taken into account. 

The presence of certain chemical elements of lesser biological im- 
portance has been announced from time to time in a group of papers 
which have some interest, although it is difficult to see, as yet, what 
their importance is for the development of the embryo. Fluorine has 
been estimated by Tammann and by Nickles, copper by Dhere, 
boron by Bertrand & Agulhon, manganese by Bertrand & Medigre- 
ceanu, iodine by Bonnanni and by von Fellenberg, lead by Bishop. 

These elements appear to be normal constituents of the egg. The 
iron-content can be artificially increased by feeding iron-rich rations 
to the hen, and iodine can also be introduced into the egg in this way, 
as has been done by Bonnanni, Kreis and others, but Hofmann found 
that though iron and iodine would enter the egg thus, it was impossible 
to get copper to do so. In just the same way Ricci found it difficult 
if not impossible to get As or Hg into the hen's egg by feeding sub- 
toxic doses to the hen. The normal copper-content of the hen's egg 
cannot be varied like its iron-content. The importance of iron in 
the formation of haemoglobin is obvious, and the little that is 
known about this process will be discussed in the section on pigments 
in the embryo. Wassermann made a histochemical examination 
of the egg-yolk and vitelline membrane for iron, and found a 
relationship between the embryonic blood-islands and the iron of 
the yolk. 

Some of the other data in Table 28 call for comment, Tammann's 
1-13 mgm. per cent, fluorine in the fresh yolk works out at a quantity 
of 0-2 mgm. per egg, and, as Zaleski found 0-23 per cent, fluorine 
in the bones of the chick at hatching, o-o8 mgm. fluorine would be 
required in the egg at the beginning, or less than half of what is 
actually there. Zaleski's figure, however, is old, and may be too low. 
It would appear, on the whole, as if the greater part of the fluorine, 
iodine, copper, zinc, lead, aluminium, silicon and manganese is 
localised in the yolk, and the greater part of the boron and arsenic in 
the white. In view of the importance which we now attribute to these 
less common elements as catalysts in living tissues, this distribution 
may be found to have considerable significance. 




Pi ^ 



























^ ^ 

.« " 

^._, en «J 
3 <^ >-i ir! 

^ c «e ^ 

O^ o 



„ a 


.23 w 

w 5<^ 

3 -" 

_>. « 


"rt CU 




o . , bD 



SU > m 

-d „ -0-3 

o o o o 

c ^ 

F « 

S bD 

C; V3 C3 



O CO ^-- 

o o •■ 

?? " 

-. CI " O o r-» - 
o o o o o o o 
6 6 6 6 6 6 6 

5 =a 


^ s 

^..— V 

c^ S 

.-, lo 

1-1 v!l CI 

--^ f. W 

c>! nj'^ 

Wolff (19 



Fleurent i 



.-S-S 1 

6 6 oi 6 

? I 


h K 



S 2 








^ ^ 

,. ^ 








W n 




i-4 « 









„, — ,. '- ^ 



cn r. 






CTi ^ ... 





o - >-■ »3 


S-i '• 

J, ci 

«^ it: ^ rt 





^^ S-^ 

Oh cq M 

6 6 

« cq cq>Mm CLiOiiq Q 

^ ^ ^ Oi ^ o 





o o 




(UN-" HP^ 

^ o -^ 
= ^0^:2. o- 

_C ^ '^ '-I — ' 

P ^ c^ 


6 Oh 

•£ bo 

?2 o 


tj t? 


CTlCO ^ 



6 6 - 1 



6 6 




<p c3 












lU "O 


^ s 


.S ^ 










u C 


3 U 









■ — ^ 

"In. S3 




I I 

ffi ffi K 

S 3 S 

^ < 

■^ B 
c3 c S 

^ V 1;; 

O bCc 

o ^ S 

c w 
bo JJ b 



U 3 4-> 

;-> u c4 

c S-5 

o ex ,„ 

c_> n 5" 


t, « 5 
.§■« 3 

fci ■" CX 

bo c -3 


The figures which have been obtained by those investigators 
who have examined the iron-content of eggs are seen in Table 29. 
All found a great deal more iron in the yolk than in the white, 
as might have been expected from the earlier micro-chemical 
researches of Tirmann and Kobert. This kind of work had been 
originated by Schmiechovski, and was continued later by Wasser- 
mann in the interesting paper already referred to. Schmiechovski 
found iron histochemically throughout the yolk, but considered that, 
in the white or milky yolk, it was confined to the megaspheres. 

Table 29* Iron in hen's eggs. 

Italic figures indicate dry weight data. 
FcaOs gm. % wet weight 

Without iron-rich diet With iron-rich diet 

, ' ^ r ^ ^ 

Egg-white Egg-white 

Egg- plus Egg- plus 

white Yolk yolk Shell white Yolk yolk Shell Investigator and date 

•0024 -0088 -0047 -0272 -0040 'oogs -0059 -0272 Loges & Pingel (1901) 

— — -0046 — — — -0040 — Kreis (1900) 
•0057 -026 •0165 — — — — ^ Lebbin (1900) 
■03 -05 -03 _____ 

•001 12 -00995 '00425 — — — — — Hartung (Mar. 1902) 

•00087 -01106 -00451 — — — — — ,, (May 1902) 

— — — — -00208 -01621 -00729 — ,, (June 1902) 
Trace -0108 — — — — — — Bunge (1892) 

— -0121 -0018 — — '0175 -0032 — Hofmann (1901) 

— -;r -0057 — — — — — Boussingault (1850) 

— -063 -og§ — — — — — Leveque & von 

Tschermak (191 3) 
None 'OI43 — — None '0143 — — Elvehjem, Kemmerer, 

Hart, & Halpin (1929) 

Wassermann, using both the ammonium sulphide and the Berlin 
blue methods, decided that it was present in both kinds of yolk, 
but that it was not confined to those special elements in the white 
part. In fact, it was very much more abundant in the white than 
in the yellow part. This finding has never been corroborated by 
chemical analysis, but, if it is, it will have considerable importance, 
in view of the time at which haemoglobin is most vigorously manu- 
factured by the embryo. For a further discussion of these questions 
see the section on pigments. 

i-ii. General Characteristics of Non- Avian Eggs 

With this we may conclude the discussion of what is known 
about the typically terrestrial egg, that of the bird. Now 


aquatic species far outnumber the terrestrial ones; as Spenser 
put it: 

O ! What an endlesse Worke have I in hand 

To count the sea's abundant progeny, 
Whose fruitfull seede farre passeth those on land, 

And also those which wonne in th' azure sky: 
For much more eath to tell the starres on hy, 

Albe they endlesse seeme in estimation, 
Than to recount the sea's posterity. 

So fertile be the flouds in generation, 

So huge their numbers, and so numberlesse their nation. 

It might therefore be supposed that a much greater space would 
have to be devoted to their eggs than what has already been taken 
up, but this is not the case, for the bird's egg has been so convenient 
a material for research that the knowledge we have of it outweighs 
that of the eggs of all other animals put together. Indeed, the data 
about the eggs of other groups are very fragmentary, so that much 
caution has to be used in making comparisons, and general relation- 
ships are much more difficult to enunciate. Van Beneden's classical 
memoir may be recommended as an account of the morphology of 
the eggs which are to be mentioned, and it is hardly necessary to 
refer to Balfour's book on comparative embryology. 

If Table 30 is examined, and compared with Table 2, it will at 
once be seen that the percentage composition of eggs of other classes 
of animals differs markedly and in very definite ways from the egg 
of the hen. The case of reptiles may first be taken, as being less remote 
than others. The reptilian egg seems to be distinctly drier than that 
of the bird, by about 20 per cent., and much more variable in its 
fat/protein ratio. For, while in all birds' eggs that have been in- 
vestigated, the amount of protein, whether related to dry or to wet 
weight, is about the same as that of fat, the reptilian egg shows big 
variations from this rule. In the eggs of the tortoise and lizard, for 
example, there is twice as much protein as fat, while in those of the 
grass-snake, studied by Galimard, there is three times as much fat 
as protein. This fact will be mentioned again later (see p. 313). 
Considerably more is known however about those of amphibia, 
which have also been found to contain a great deal more protein 
than fat. Thus, instead of the 40 per cent, protein and the 40 per 
cent, fat which make up the dry substance of the hen's egg, Faure- 

N " 

3-— -_-N 

■5 ^M 

'o >^ 

2 S 

C ■ H 

£ 3 K 


53 fc 3 rx t c -a 


*;--- o o 











snjoqdsoqd I | 


ajqegtuodESun iejoj^ | | 

I0J3jsa]0H3 I I 





do 6 b> « 

uiajojj I o 


aSa am JO iqSia^ 

f^ f-* b* 

li^ i^ mvo ID tD 

lira a 

s s '^ 

o -SS 



C V C >; 

Itil t 

« « c « a 
c c c c c 
s c a c c 

Kc bi be M en 
0000 - o 

tc Uc Vh I- ' >-i 

2 2 ^ 

oC;'S^ o'o.Ji 


^:3 2 


T3 Ca 
N — ^ t-, o f- ^ ^ , 


^— P- 15 

c 3 O O 

'E C N li 

CSS « 

H >^ 

- "I I* ffl>^"0 o 
5J C ij!!0.>Sl fc 

<3 •* 

o pn 00 
n t^ O r^ 

b>cb b b* 

op ^00 00 

00 M N>0 

ri inb'b 

■* N OO O- 

l/l w N 

O " o 

00 '-' O' ro O 

QC 00 30 O 1^00 

00 00 00 

■*vO « 00 o 

o "i-oo o 
b " 6 N 

O f^ I 00 N rf C 

poo PJ 

00 M N 

t^OO OM^ O N 

f^ iri f*^ r^ f^O m b^ 

COO OO 00 N O' N O 

00 r^ o 00 c , N 
N N\b b CO r*) 

CM^ Tj- iri sO sO 

o> N o o t^ 

1^ o 


r^ O^ f^ 
N f^ ^ 

b.M « 

o ■^oo fn 
H^ io f^ b* 
11 N N N 

O' 'j- O 30 

6 b " ^ 

N 't ^ in 

m\0 N (vj 
f^ inOO V 

on in Tj- o ui 

O o \0 M in ^ r^ 

'noo M r^ O'O oo 

\0 -^ in in r^ ^oo 

tn tm 

5 aOl 


Omen OU O 


S'^ '^ . -s 


hcuHHE-' E-h 

• c o 
.■5 ^ 

'-'^^-^ JJ — 

c^ QQQ C 

o ^ 










ua3oj}Tjsj I I 





spiodiq I I 

qsy o op 






333 aqj jo jqSp^ | | 

moo m N f^ m * 

•<J-vO O O t~ 

N o ino \0 o o 

p p o o o o o 
b b b b b b b 

T)-o o^o o o o o 

b ^ " boovo b t^ 
t^ £^ t^ r^^ m^o vt 

1 I I I I I I I 

■~ 1-1 ii 

« 2 "s ? 3 ^ 

£3 r r 

w O .'t! ^ -^ 

0, -s^ 

Q Q m fl^^UKPQ 

.2S o^'i-ii-a 


w 0^= 

•a • 


c.E-S 0.1 

3 M 
O C 


0) u cs 3 0*^ 





« .s 

M _ - ?> C 00 ^ 


-^ 1 




1? °~ ^ 




N It 



rov (188 
Conte ( 
rcmiet & 

wOO N 

,_, o 






E p5 


s 5 

fc^ b 

o O I 1 

A A 


° I 

N 0* 
N 6 

U1 r» 1 
o o 
b b 

S 5 s s 


US « 







••* a-»* 







c c c 


^— ' 



»■ u u u 

3 3 3 


!<! « « 




I 5 a S 

^ OS 03 

s ^. a ^ 

•- :2 

4) 55 ^ 

-a ~ ■= 

<; b J 


S 2 



"55 S 

9 E 

Z 3 


Fremiet & Dragoiu found the dry material of the egg of the frog to 
consist of 60 per cent, protein and only 14 per cent. fat. And this has 
been the experience of all those who have analysed amphibian eggs. 
Next to the hen's egg, the eggs of fishes have probably received 
the most attention. The recorded analytical figures for fish eggs are 
often deceptive, for many analyses have been made of salted fish 
roes and egg-preparations such as caviar, but the greatest care has 
been taken not to include in Table 30 results which might have been 
vitiated in that way. The question is complicated by the fact that 
analyses of the purified constituent egg-substances prepared from 
preserved material may well be admitted into consideration, for, 
except in certain cases, they would probably not undergo much 
change during the process of preservation. As in the case of reptiles 
and amphibia, the fish egg is characterised by its predominance of 
proteins as the food of the growing embryo. It should be remembered 
that, in all these comparisons, the yolk of the hen's egg is a more 
proper standard of reference than the whole egg-contents, in which 
case the differences become even more remarkable. This generalisa- 
tion appears at all points; thus, the brook-trout, a fresh-water fish, 
has 30 per cent, of protein and only 9 per cent, of fat, and the herring 
has 26 per cent, as against 3 per cent. In Table 31 the protein/fat 
ratios are collected together, and the difference emerges there with 
great clearness. Though it is obvious that fishes vary considerably 
among themselves as to the fat-content of their eggs, yet all of 
them have more protein than fat. The only fishes in Table 31 
which come near to being exceptions to this rule are the sturgeon 
and the dogfish, both of which have an unusually high amount of 
fat in their eggs (a fact which accounts for the superiority of Russian 
caviar over other varieties, for the former is made chiefly from the 
eggs of sturgeon) . Besides this general difference between the egg of 
the bird and that of the fish, there are many others, but they concern 
the chemistry of the individual components rather than the rough 
constitution of the egg as a whole, and will, therefore, be dealt with 
later on. If Table 31 be further studied, it will be seen that, as far as 
can be known at present from the few analyses of crustacean and 
cephalopod eggs, the superior proportion of protein over fat holds 
good there also. Curiously enough, the only analysis we have for 
a gastropod egg gives a picture more resembling the egg of the hen, 
comparatively equal amounts of fat and protein being present. 

SECT. l] 



The position of affairs may perhaps be summarised by saying that 
it is only the birds which have been successful in producing an egg 
really well stocked with fat, though the reptiles clearly show an 
approximation to this achievement. Does this mean that the storage 
of fat in the egg is particularly associated with terrestrial embryos? 
The facts and arguments to be brought forward in later chapters (see 
Sections 7-7, 9-15 and 1 1-8) make this hypothesis a very likely one, but, 
as Table 31 shows, the silkworm (the only representative of terrestrial 

Table 31. Protein/ fat ratio in various eggs. 




Hen (yolk) 
„ (whole egg) 







































arthropods) does not seem to have succeeded in storing fat in its 
egg to any great extent. It might, of course, be argued that this was 
one of the factors which prevented the insects attaining any con- 
siderable size and rivaling reptiles and mammals for the possession 
of the land. The mammals gave up the heavy fat storage in the egg 
when they invented viviparity and the fully developed placenta. In 


this connection the monotreme egg would be a chemical study of 
great interest, and it is characteristic of the exasperating fragmenta- 
tion of this field of work that all we know about the monotreme egg 
is that its membrane seems to have the properties of a keratin. The 
suggestion that the metabolism of the fowl, operating on a con- 
tinuously high level of energy turnover, would naturally tend to fill 
up the eggs with fat, and is associated with the well-known higher 
temperature of the avian body (Wetmore) may not be without value, 
but any special emphasis on fat metabolism in adult birds is precluded 
by the statements in Schulz's review. 

It is very significant that as animals became more complicated and 
more adaptable to varied surroundings, higher, in fact, in the taxo- 
nomic scale, they loaded their eggs to a greater extent with yolk. Since 
the extra material was usually fatty acids, this process appears 
strikingly in Table 31 . The effects of the yolk have long been familiar 
to embryologists, and have been best described, perhaps, in a passage 
by Milnes-Marshall. "The immediate effect of a large amount of 
yolk", he said, "is to retard mechanically the processes of develop- 
ment, but the ultimate result is to shorten them. This paradox is 
readily explained. A small egg, such as that of Amphioxus, starts its 
development rapidly, and in about eighteen hours gives rise to a 
free-swimming larva, capable of independent existence, with a 
digestive cavity and a nervous system already formed ; while a large 
egg such as that of the hen, hampered by the great mass of yolk 
by which it is distended, has, in the same time, made very little 
progress. From this time onwards, however, other considerations 
begin to tell. Amphioxus has been able to make this rapid start owing 
to its relative freedom from yolk, but now this freedom becomes a 
retarding influence, for the larva, containing within itself but a very 
scanty supply of nourishment, must devote much of its energies to 
hunting for and to digesting, its food, and hence its further develop- 
ment will proceed more slowly. The chick embryo on the other hand 
has an abundant supply of food in the egg itself and has no occasion, 
therefore, to spend its time searching for it, but can devote its whole 
energies to the further stages of its development. Hence, except in 
the earliest stages, the chick develops more rapidly than Amphioxus 
and attains its adult form in a much shorter time. The tendency of 
abundant yolk to lead to shortening or omission of the ancestral 
history, is well known. The embryo of forms well provided with yolk 


takes short cuts in its development, and jumps from branch to branch 
of its genealogical tree instead of climbing steadily upwards. Thus 
the little West Indian frog, Hylodes, produces eggs which contain a 
larger amount of yolk than those of the ordinary English frog. The 
young Hylodes is consequently enabled to pass through the tadpole 
stage before hatching, and to attain the form of the frog before leaving 
the c:gg\ the tadpole stage is, in fact, only imperfectly recapitulated, 
the formation of gills, for instance, being entirely omitted." 

The more yolk, then, the longer the embryo can remain an embryo 
before having to face the external world, and the more preparations 
it can make for that event. It is probable that this question is 
intimately bound up with the penetration of fresh-water surroundings 
by the originally marine forms. "It has long been noticed", said 
Milnes-Marshall, following the classical exposition of Sollas, " that 
marine animals lay small eggs whereas their fresh-water allies 
lay eggs of much larger size. The eggs of the salmon or trout are 
much larger than those of the cod or the herring, and the crayfish, 
though only a quarter the length of the lobster, lays eggs of 
actually larger size. The larger size of the eggs of the fresh-water 
forms appears to be dependent on the nature of the environment 
to which they are exposed. Considering the geological instability 
of the land as compared with the ocean, there can be no doubt that 
the fresh-water fauna is, speaking generally, derived from the 
marine fauna, and the great problem with regard to fresh-water life 
is to explain why it is that so many groups of animals which flourish 
abundantly in the sea should have failed to establish themselves in 
fresh water. Sponges and Coelenterates abound in the sea, but their 
fresh- water representatives are extremely few in number; Echino- 
derms are exclusively marine ; there are no fresh-water Cephalopods, 
no Ascidians, and of the smaller groups of Worms, Molluscs, and 
Crustacea, there are many that do not occur in fresh water. Direct 
experiment has shown that in many cases this distribution is not due 
to the inability of the adult animals to live in fresh water, and the 
real explanation appears to be that the early larval stages are unable 
to establish themselves under such conditions. To establish itself in 
fresh water permanently an animal must either be fixed, or else 
be strong enough to withstand and make headway against the cur- 
rents of the streams or rivers it inhabits, for otherwise it will in the 
long run be swept out to sea, and this condition applies to larval 


forms equally with adults. The majority of marine invertebrates leave 
the egg as minute ciliated larvae, which are quite incapable of holding 
their own in currents of any strength. Hence it is only forms which 
have got rid of the free-swimming ciliated larval stage, and which 
leave the egg as organisms of considerable size and strength, that can 
establish themselves as fresh-water animals. This is effected most 
readily by the acquisition of yolk — hence the large size of the eggs of 
fresh-water animals — and is often supplemented by special devices." 

Here is an explanation for the well-known paucity of eggs in fresh- 
water plankton. In certain cases it is possible to induce an embryo 
to skip the larval stage which it should normally pass through. Thus 
Child could abolish the free-swimming larval stage in the ascidian 
Corella willmeriana, simply by removing the eggs from the parental 
atrial chamber {p¥L j'^.) to normal sea-water (/>H 8-4). 

Giard had also noticed the discrepancy in egg-size between closely 
related marine and fresh-water forms, and had classed it among those 
cases where like adults have unlike larvae ("Poecilogony"). The 
classical instance is perhaps that of the shrimp Palaemonetes varians, 
one variety of which {microgenitor) lives in the sea near Wimereux 
and has eggs 0-5 mm. diam. (32 1 per female) and another of which 
{macro genitor) lives in fresh water at Naples and has eggs 1-5 mm. 
diam. (25 per female). Giard has reviewed this subject in a very 
interesting paper. "Dans un groupe determine", he said {(Euvres 
diverses, p. 18), "la condensation embryogenique va en croissant des 
types marins aux types d'eau douce ou terrestres." 

The correlated proposition, namely, that the fresh-water forms 
generally lay fewer eggs than the marine ones, is illustrated by the 
following instances collected by Carpenter: 

No. of eggs laid per female per annum 


Lamellibranchs ... 


Marine form 
Ostrea edulis i ,800,000 

Buccinum undatum 12,000 

Haddock 9,000,000 
Lobster 5,000 

Fresh-water form 
Uniopictorum 220,000 
Anodonta cygnea 18,000 
Average of many snails 100 
Average of many limpets 6 
Ovoviviparous pond-snails 15 
Brook-trout 750 
Crayfish 200 

Another reason for the poverty of fresh-water fauna was suggested 
by von Martens who pointed out that the fresh-water climate, with 
its periods of desiccation and freezing, was much more severe than 


that of the sea. But even these two causes together cannot fully 
account for the phenomenon, for there are many cases of individual 
species which they will not cover; thus the Cephalopods, which hatch 
out as minute but very active copies of their parents, i.e. which pass 
their larval stage within the egg, and which should therefore be 
immune from the disadvantage described by Sollas, never penetrated 
into fresh water. 

A third reason must be added to those of Sollas and of von Martens. 
As will be shown in Sections 12 and 13 the marine invertebrate embryo 
depends largely on the salts of the sea water for its supply of ash, and 
therefore could not be expected to develop in a medium very poor 
in inorganic matter. Colonisation of the fresh water could not occur, 
then, until animals had begun to provide in each egg sufficient ash 
to make one finished embryo. There seem to be few data concerning 
the capacity of marine invertebrate eggs to develop in fresh water, 
although the adult animals have been found often enough to ac- 
custom themselves to a fresh-water environment (see the instances 
given in Semper) . Many studies of the effect of hypotonic solutions 
on marine embryos can, however, be called to mind, and in all the 
cases the results are teratogenic. 

The fate of the Cephalopods, it is interesting to note, is explained 
by this third factor, for Ranzi has demonstrated the intake of the 
salts in the sea water by the octopus egg. 

As for the general statement that animals can afford their young 
a better chance of survival by providing them with larger amounts 
of yolk and therefore a longer incubation-period, there is a striking 
parallel here with the seeds of leguminous plants which are packed 
with nourishment. In the Origin of Species (6th ed. p. 56), Darwin 
wrote, "From the strong growth of young plants produced from such 
seeds as peas and beans when sown in the midst of long grass, it may 
be suspected that the chief use of the nutriment in the seed is to 
favour the growth of the seedlings, whilst struggling with other 
plants growing vigorously all round". 

It is interesting that the birds show an adaptation exactly similar to 
the poecilogony of the invertebrates and fishes. Tree-nesting birds are 
usually nidicolous, but the defenceless state of the newly-hatched squab 
has brought it about that ground-nesting birds are usually nidifugous. 

As Table 30 shows, the composition of the eggs of all animals other 
than those of the frog, the silkworm, and certain fishes, is still, to 


use a phrase of William Harvey's, "hid in obscurity and deep night". 
It is as yet much too early to try to draw any conclusions from the 
very fragmentary figures which are all that we have at our disposal, 
and we may well admit that one of the most urgent needs of chemical 
embryology is a much wider extension of our knowledge of the static 
chemistry of the egg. This is a quite indispensable preliminary to the 
investigation of the metabolism of the embryo in the lesser known 
forms. The attempt has already once been made to link up in some 
way the chemistry of the egg with what is known of the type of 
embryonic development which takes place in it. Wetzel in 1907 
analysed the eggs of a sea-urchin, a crab, a cephalopod, and an 
elasmobranch fish. He pointed out that the eggs he studied 
were examples of varying richness in yolk, of total and partial, 
equal and unequal, superficial and discoidal cleavage, as well as 
chemical systems. Taking the egg of Strongylocentrotus lividus as 
his first case, he regarded it as typical of a class of alecithic 
eggs, of a total and equal cleavage type, and he drew attention 
to the fact that it was rich in water and in salts, but poor in 
fatty substances, in nitrogen, and in phosphorus. Similarly, in the 
case of the mollusca, where there is no very definite type of 
development, the egg of Sepia could not stand as representative of 
any wider class than the cephalopods, but, as far as it went, it 
showed that the cephalopod egg was rich in nitrogen, poor in fat and 
inorganic substances, with a moderate phosphorus and water-content. 
The decapod Crustacea, to which Maia squinado belongs, have a 
purely superficial type of cleavage, with no cell-multiplication in that 
part of the egg which holds the yolk. Accordingly, the egg possessed 
a moderate fat and water-content, a moderate ash, and much protein 
and phosphorus. 

The mammalian ovum is still as unknown chemically as it was 
when Wetzel was writing, and it may be found to have a 
constitution not unlike the alecithic echinoderm eggs. For the 
eggs of birds (and of reptiles, which only differ from them in 
having very little egg-white) Wetzel found a low protein and 
water-content, a high proportion of fat and ash, and a large amount 
of calcium and phosphorus. Here cleavage would only take place 
at one isolated point on the surface of the mass of food-material. 
In the amphibia, the richness of yolk, while much more significant 
than in lower classes, does not reach the level of birds and reptiles. 


and this is duly reflected in the chemical composition by the moderate 
water-content, the high proportion of protein which is yet only 
double that of the fat. The case of the dogfish is again different, for 
there the egg is rich in yolk and the cleavage is meroblastic; thus 
the water is rather low, the fat rather high, the nitrogen very high, 
and the ash and phosphorus moderate. 

But these conclusions of Wetzel's, interesting though they are, can- 
not really be assessed until a great deal more comparative work has 
been done. They must rather be taken to represent the kind of cor- 
relation we may hope for in the future. However, one of Wetzel's 
generalisations may be accepted, if with some reserve. He pointed 
out that the fat-content of eggs showed great variations, rising from 
12 per cent, of the dry weight of the Sepia ^gg to 66 per cent, of the 
dry weight of the (yolk of the) hen's tgg. Again, the nitrogen 
gave very variable results, rising from 5-3 per cent, of the dry 
weight in the (yolk of the) hen's ^gg to 6-9 per cent, in the egg 
of the grass-snake, 1 2 per cent, in the egg of the dogfish, and even 
in the case of the cod 14 per cent. On the other hand, the phosphorus- 
content varied only between the (outside) limits of 2 • i per cent, for 
the sea-urchin tgg and 3-6 per cent, for that of the grass-snake. 
Wetzel, therefore, suggested that a distinction might be made, at any 
rate, roughly, between those constituents of the egg which may serve 
as sources of energy for the growing embryo, and those which in 
no circumstances do so. Protein, fat, and carbohydrate would come 
in the former class; phosphorus (for nucleoprotein) and cholesterol, 
for example, would come in the latter class. The former would show 
great variations among eggs of different species, the latter would not. 
He thus supposed that one might be able to deduce, as it were, the 
constitution of any given egg, if one knew what substances, and in 
what proportions, were used by the embryo as combustible material 
during its development, as well as the constitution of the newly born 
or hatched organism. 

From this standpoint Wetzel distinguished four types of substances 
in the unincubated egg : ( i ) material for the embryo to burn during 
the course of its development, (2) constituents of the finished proto- 
plasm of the embryo, (3) constituents of the finished embryo, but 
not for incorporation into the protoplasm itself, but into the para- 
plasm (in Le Breton's terminology), (4) the protoplasm of the original 
egg-cell. No aspect of chemical embryology needs attention more 


urgently than this, and the correlation of chemical constitution with 
developmental type should offer a most attractive field for research. 

But it is not only correlations of this type that lie hidden under 
the enigmatic character of analytical figures. The water-content of 
the eggs may have a powerful effect on the sex-ratio, for King found 
in 191 2 that reducing the water-content of fertilised frog's eggs con- 
siderably lowered the proportion of males, while increasing it by 
means of treatment with dilute acid considerably raised the pro- 
portion. A discussion of these facts in relation to genetics as a whole 
will be found in the review of Huxley. It is probable that the effect 
which delayed fertilisation has upon the sex-ratio is to be explained 
by difference in water-content of the eggs. Hertwig was the first to 
observe this delayed fertilisation phenomenon in some work which 
he published in 1905, and since then it has many times been observed 
not only for amphibia but also for trout (Kuschakevitsch; Huxley; 
Mrsic) . Riddle has suggested that the mammalian egg may be subject 
to such influences as it passes from ovary to uterus. He quotes van 
der Stricht's histological work on the bat's egg during this process, 
and points out that the swelling of the yolk-granules would indicate 
an absorption of water. The exact degree of hydration of the mam- 
malian egg might thus conceivably have an effect on the mammalian 

Table 30 has several more important points which have not, so 
far, been touched upon. It is interesting to follow in the figures of 
Milroy the difference between the fish eggs which float at the surface 
of the water during their development (pelagic ova), and those which 
sink, or rather float, at lower and denser levels (demersal ova) — 
the former have a water-content of about 90 per cent., the latter of 
about 70 per cent. A knowledge of the chemical composition of fish 
eggs throws a great deal of light upon their distribution in the sea, 
and so indirectly upon ecological problems. Their fat-content, for 
example, has been treated from this point of view by Polimanti, whose 
work will be discussed in the section on the general metabolism 
of the embryo; and the investigations of the specific gravity of fish 
eggs, which are discussed in Section 5, have also an important 
bearing upon these problems. Another point worth notice is the 
approximately constant percentage of cholesterol in different eggs, 
nearly always about 500 mgm. per cent, of the wet weight, a pro- 
portion which, roughly speaking, holds for the egg of the hen as well. 


It would be as well to emphasise the fact that no principle of selec- 
tion has been used in the preparation of Table 30, on the ground 
that results such as those of Roffo & Correa on a Brazilian gastropod, 
and McCrudden on fresh-water fishes, which seem obviously wrong, 
may not be so at all. The estimation methods and analytical processes 
which are by general consent judged most satisfactory at the present 
time cannot be considered in any way final, and to have excluded 
certain results on account of the technique employed in obtaining 
them would not have been justifiable. Table 30 does not, therefore, 
absolve investigators fi'om the duty of looking up the original papers 
in such cases as touch them most closely, and forming an independent 
judgment, according to the best opinion of the time, on the stress 
which can be laid upon them. It is needless to say that I leave out 
of account all doubtful figures in the generalisations made here. 

I -12. Egg-shells and Egg-membranes 

Very little is known about the relative proportions of yolk, white, 
and shell, in the eggs of the lower animals, or rather, in most cases, 
egg-contents and shell or surrounding membrane. Table 32 gives a 
few figures. The discrepancy between the results of Ford & Thorpe, 
on the one hand, and Wetzel, on the other, is very strange, especially 
as they both used Scyllium canicula eggs, but it is probably due to 
insufficiency of the statistical element. Ford & Thorpe's proportions 
are more likely to be accurate. 

Much work, however, has been done on the membranes and hard 
coverings which invest the unincubated eggs of diflferent kinds of 
animals. For instance, the gelatinous substance which surrounds the 
undeveloped amphibian egg was examined chemically by Brande 
in 1 810, who noticed that it absorbed water and was not precipitated 
by tannin or by strong acids. Later work has shown that it consists 
almost entirely of mucoprotein and water. Wetzel's figures for its 
weight are shown in Table 32. Giacosa isolated mucin in a pure 
state from it in 1882, and the figures which he obtained for its per- 
centage composition are shown in Table 33. He was able to show 
the presence of a reducing sugar on hydrolysis, but he could 
isolate nothing else from the jelly, and therefore concluded that 
it was pure mucin. The presence of glucosamine in the muco- 
protein was afterwards confirmed by Hammarsten, by Schulz & 
Ditthorn and by Wolfenden, who confirmed Giacosa's finding that 



[PT. Ill 

Table 32. 

In % of total egg-weight 




Carp ... 
Cod ... 
Pike ... 





8-87 (wet) 


Trout ... 

25-97 (dry) 


Yolk Investigator and date 

— Konig & Grossfeld (191 3) 

3? 33 

75-3 Ford & Thorpe (1920) 
36-5 Wetzel (1907) 
— Tichomirov (1882) 



Kronfeld & Scheminzki (1926) 
Ranzi (1930) 

Tomita's figures. 

Marine turtle ( Thalassochelys cortica) 





m gm. 








Wetzel's figures. 

I Frog {Rana temporaria) 

Ovarial egg (no jelly)... 
Egg with unswoUen jelly 
Jelly alone 
Swollen jelly ... 
Water content of ovarial egg 
„ „ egg and jelly 

Empty dry jelly 
Dry egg 

Dry egg + dry jelly ... 

Thus of dry weight egg 


Weight in mg. 






Melvin's figures. 

Shell-weights of insects 

Squash-bug {Anasa tristis) 
Luna moth [Tropoeoa luna) 
Cecropia moth {Sarnia cecropia) ... 
Smartweed-borer {Pyrausta ainsleii) 





% of total 

weight of eggs 



it was remarkably resistant to putrefaction, and studied the 
effect of enzymes such as pepsin upon it. The resistance of 
frog ovomucin to putrefaction was for long a puzzle to bio- 
chemists, but it seems to be explained by the unwillingness of most 


bacteria to grow on pure proteins, and as the jelly contains no 
enzymes of an autolytic character no protein breakdown products 
are formed, and consequently no bacterial growth takes place. This 
might be considered a protection of the developing embryo from 
bacterial attack. It is very probable, moreover, that the mucoprotein 
acts as a source of nourishment for the young tadpoles immediately 
after hatching, for they invariably attach themselves to it after they 
emerge from the egg-membrane, and hang on to it by their oral 
suckers (for histological details consult Nussbaum and Lebrun). On 
the other hand, development will readily proceed in the absence of 
the jelly, for as Hluchovski has shown it is disintegrated by exposure 
to ultra-violet light and may thus be removed without harming the 

The swelling which takes place in the gelatinous covering when 
the eggs are shed into the water was studied as long ago as 1824 
by Prevost & Dumas, who measured the size of the eggs at intervals 
after they were laid. Their table is as follows : 

Hours after laying 

Diameter of egg (mm.) 














They observed that dyes would pass through the jelly as soon as 
it had swollen, but not before. Similar work by Wintrebert on 
Discoglossus pinctus gave the following figures : 

after laying 

Diameter of egg (mm, 


2-5 X 2-3 


3-0 X 2-7 


3-3 X 3-0 


5-8 X 3-2 



As regards the mineralogical and morphological structure of the 
egg-shells of the lower animals, a good deal is known, and for full 
detail the reviews of Prenant and of Biedermann should be referred 
to. The majority of reptile egg-shells have their calcium carbonate 
in the form of calcite, as Kelly; Schmidtt, and Meigen have shown, 
but the two first-named investigators discovered that the tgg- 
sheUs of chelonia were of aragonite, and later Lacroix observed 
a similar phenomenon in the case of certain saurians. The tgg- 



»-l ^-v 


plH lO 




V5 ,— ,0^ 



cco_i B 


'0 cS "C 


S fe S E 

-= '*;i: 3 

cS r3 k! u 


|i| CO 


i^ ^ ?, 

- o S- 




co^ cr 

■" ^ fi 

i- -> S 

w JJ p 

U . S V! 

C3 O O^ O 

Cj :0 







> ffi 







V V 

- <u 

c c 


(U V 


> > 


u u 




■^ (S CO 

f~. i^ r^ 

CD ^ 6 
Th' lO m 

1 1 1 ^ 1 

1 1 ^ LO O) 

■^ 1 

1 1 1 Tj- 1 

1 1 ^ 01 CO 

S (N <N 


tr> CO "^ 

-co locf J^ 

•^ CO 

CO 6 ' ' '-' 

066 i-l 

Ci 6 


1 CO (M y 01 

CO cog CO 

coo <>' 
CO r^CT^T** 


CO « 

6 -H - 

6 « 6 

6 6 


CO ix> ■* 0^^ 

«3 CO 


CO inOi ^ "^ 

lO lO io 10 tJ" 

N4 »-t 


1 1 r^ 1 

m loco 
1 1 CO ^90 


1 1 f,.r- 1 

' ' f^f- f^ 


1 1 ^"^ 1 

1 1 " ^^ 

CO to 

1 1 04 CO 1 

\ 1 COM CO 
lO lO 10 

Tf" CO 

II I ^ 

COtO COCO " lOTfOO,"- 

r^ lO lO r- f^ O CO '^'-o <-0 

O O " o o 

O " o o 

6 "^ lO lo rhco 
r~- 01 coto COCO 

" coco 


(O 10 in loto CO I oy^irS^l 2L^~ 
a)iocr)"-*o< I o^inpr^l ^'TP 
o«o»-'"" i,M«i-<i-i 000 

inoj 00050 -^o o^5< ;*co eo eo 


o o •* Oi 
r-~ o CO CO 
(O coco <o 

r^to m 

I T^jH in CO 

I 01 0) 01 

irj eo CO 

S- - ^ lij i^ 



_c j^xi a, 

3 o 3 

-Cl -fi -TJ cj 

3 S 

-s y 

.^-S 3 


:-yS .SJ^ 

fc. Q. lU .. 









3 <u.y 



1— 1 



P ^-5 3 

(I 3 

lU 3 T3 

3 p c« 

: § a o.g .0 cs 
c'3 g''3'3^-" 



us b 

<i "^ r^ 





7. :: 

m « iS- 

< r. 

u ^ 

►- 2 




CO s 




Q. — ' 

< 2 




s . 

. S 

,« • 



M 3 0, fcj 


• 3 



Co • 
W)--^ bo 

c « S - ^ 

•"CTs-i CT3 t^TJ >>u J; 
S « t, O^ O t« c« u 



11 O tJ< 

CO CO 01 

" c^ c< 
C be rt 


c3 « O 

3 3 g 




^ ^co 

.^^ 01 CI 


o w c 

2 M O o 

" u 

o >S9 
►" t< " 

ea o 

w O bo 

JS CO '-' 
+3 ^ ^ 

(-, bD 3 
o C t; 

O lO 10 

O) o 

0» Tt" 


o o 

CO lO x^ 

■*co o 

O c< ij* 

CI ^ 
U 0< CO" t~-T}<T}>C5-* 




O ■<t' C< coco '-' t^'O C5 lO O coco 1^ I I I I 
CT> •* LO COK3 CD ii CTlCO >pcp O ~ CO | | | | 

^ O o r^ CT) inco CO CO ■* -" lO •* ci 


in o< T^ Lo^i in lo ■^ -^ LO'-is -rt" ot tJ" 


coto r^Loo<^cp o< 

io io io io LOCO " t}- 

(V f^ C50 " 

CO p o( o I "- 
4f ^^ o< I ot 

I r^co 
I ^ 'p 


o UD i^ r^ 

•- lO LO 

^ CO - CD - CD CO CDco cr> 
r^ co'O ■* 10 ■-■ LO CO LO t^ 
f^ f~(i) to <i f^ r^ 1^ f^ f^ 

o c» "^ •* o >o o o CJ5 o» 
to CT> '*'-^ LO incp to CO lO 

0) CO" CO" OI^lOn « 

<o - - ei 

C^i-D CO CO 
t-D f^to to 

rt :; ;i 

J2JS "3-C 

U U - tJ K>l 

C C fl 

c c 

be— ■?!— d 









*" — — — G*"*-* C — 
3 3 3 3;S'3"3-S 3 

„^^^-c;5x-c (S-3 


« =s 

S g 



1 : :s2 

? ? 

- : 

• * C I 

1^ :2.S 

,0 -2 ^ 


a c3 

^ g^'C 



-_- :cr)a,05i>5 


« '. iS 


C •^--' 



"3 u 

bo ' he ' 

.S c « 
C &,'t^ 3 

■ 2 t« 

C "0 a; 

i- I-c IJ 

(- > 

w cs ii 





u bo 
Ki O 



— c 

a o 
z ^ 

^3 2, 
3 c , 

^ ^ 



membranes of snake's eggs which show all variations as to lime-content 
(see Table 9) are, as Kelly has shown, composed of amorphous and 
unstable calcium carbonate. The eggs of gastropods, such as Helix, 
Ampullaria, Bulimus, Amphidromus, etc., are, as Turpin {Helix aspersa) 
and Rose {Helix pomatia) , besides the workers mentioned above, have 
demonstrated, like those of birds in having their lime in the form 
of calcite. For a general theory explaining these differences see the 
paper of Prenant. 

The shells of eggs may also contain calcium phosphate. In the 
hen and in birds generally there is very little, but the globules seen 
in their egg-shells are believed to be calcium phosphate, though no 
analysis has given a figure of more than i per cent, of this salt. 
In other eggs, however, there may be more; thus Gmelin found 
7-3 per cent, in the egg-shells of a tortoise, and Kelly noted its 
presence also in those of Bulimus and Lophohelia, though she gives no 
analytical figures. 

It is interesting to note that the mineralogical form of lime in the 
egg-shell may vary during the development of the embryo; thus 
Kelly says that the shell of many full-grown mollusca is conchite, 
while that of their respective embryos and eggs is calcite. Kelly found 
that the organic substance was a remarkably constant proportion 
of the shells of mollusca, reptilia and birds (see Table 9). Some egg- 
coverings contain almost no water at all (birds), others have more 
than the egg-contents, as has been shown for the trout's egg by 
Kronfeld & Scheminzki (membrane 75 per cent., egg 66 per cent.). 

By far the commonest substance of which egg-membranes are com- 
posed is keratin, though this protein seems to take many forms, and 
not to have exactly the same properties in different situations. The 
earlier workers were content to assert the presence of it on the basis 
merely of solubility tests. Thus in 1874 Schenk studied the egg-shell of 
Raia quadrimaculata, and decided that it was 95 per cent, keratin after 
the application to it of the protein colour reactions and an examina- 
tion of its behaviour towards various solvents. The same conclusion 
was arrived at by the same methods by Hussakov & Welker for the 
egg-cases of Raia erinacea, and the Port Jackson shark, Heterodontus 
philippi. The keratin of these egg-cases was insoluble in all solvents 
except acid and alkali. They found that sulphur was present, but 
no phosphorus, and they were unable to find any reducing sugar 
after total hydrolysis. Irvine, using an optical test for chitin, found 


none in elasmobranch egg-cases. Krukenberg in 1885 decided that 
the egg-case of Scyllium stellare was of a keratinoid nature, because 
of its percentage composition, in which he found a marked amount 
of sulphur. He observed the interesting fact that the egg-cases of 
this fish, while still in the uterus of the parent animal, would dissolve 
in pepsin and trypsin, while after they were laid they would not 
dissolve in solutions of either enzyme. He also isolated tyrosine and 
leucine firom the keratin of the egg-cases of Scyllium stellare. He made 
very similar researches on the egg-cases of Scyllium canicula and 
Myliobatis aquila, finding that they possessed rather different properties 
and seemed to be of different constitution; thus on hydrolysis he 
recovered a great deal of leucine and hardly any tyrosine from the 
keratin of Scyllium canicula, while from the keratin of Myliobatis the 
yields were precisely reversed. The latter substance was also con- 
siderably more resistant to digestion than the former, and Krukenberg 
considered that the former was not a keratin at all. He had already 
decided (wrongly, as it turned out) that the shell-membrane of the 
hen's egg was mucin, not keratin, and now he concluded that this 
also applied to the egg-case oi Scyllium stellare, as well as to that ofLoligo 
vulgaris, of which he made a separate examination. He thought it 
possible also that the jelly which surrounds the egg in the ovo viviparous 
selachians might be a mucin too, especially as, according to Schenk, it 
was not precipitated by chromic acid, and he himself found that it was 
extremely resistant to digestion by enzymes. This material has received 
no further chemical investigation since the time of Krukenberg. 

Other workers who identified the proteins of egg-membranes 
by the aid of colour tests and solubility reactions were Leuckart, 
who showed, as far as anything could be shown with such preliminary 
methods, that the membranes of planarian eggs were of chitin, and 
Yoshida & Takano and Jammes & Martin, who drew a similar con- 
clusion about the coats of the eggs of Ascaris lumbricoides, which they 
found were readily soluble in gastric juice or in any acid.^ The 
case of the parasitic nematodes is of special interest, for the chitinous 
membrane does not arise until after the fertilisation of the egg, being, 
therefore, in a sense, analogous to the fertilisation membranes of 
echinoderms. Whether the chitin is formed as it is required during 
these early stages, or whether it is already present in the unfertilised 
egg-cell in some soluble form, is uncertain. Faure-Fremiet in an 

^ See also Campbell on the chitin of insect egg-membranes. 


attempt to throw light on this question, prepared pure samples of 
chitin from the newly fertilised eggs ofAscaris megalocephala by boiling 
them with strong potash, and identified the chitin chemically, 
isolating glucosamine hydrochloride from it. Remembering that 
Weinland showed that chitin is probably formed from glycogen 
during insect metamorphosis, Faure-Fremiet estimated the glycogen 
in the Ascaris eggs before and after fertilisation. Before fertilisation 
there was an average amount of 20 gm. per cent, dry weight, but 
afterwards only 4-67, the extreme values being 5-91 and 3-23, so 
that no less than 17 per cent, of glycogen had disappeared. Estima- 
tions of chitin in the egg-envelopes after fertilisation gave results of 
between 8-3 and 10-7 per cent, dry weight of glucosamine (calculated 
as glycogen) with an average of 9-23. The total glucose, then, in the 
fertilised eggs was 12-83 to 15-08, as against 20-0 in the unfertilised 
ones, a loss of 7 to 9 per cent. All the glucose lost, therefore, could 
not have transformed itself into chitin, but must have had some other 
destination, perhaps butyric and valerianic acid if Weinland's view is 
correct. The eggs o^ Ascaris have also an " ovospermatic membrane", 
but for the discussion of the significance of this reference should be 
made to the memoir of Faure-Fremiet, and nothing is known about 
it chemically. Their third membrane, the internal one, would seem 
to be composed to a large extent of ascaristerol (see p. 352), for the 
histological evidence demonstrates a collection of the ascaristerol 
globules at the periphery of the cytoplasm. After fertilisation, Faure- 
Fremiet found the saponification number of ascaristerol lowered from 
199 to 145, from which he concluded that its constitution had been 
slightly altered. Zavadovski has also described the egg-shells of many 
nematodes. • 

Neumeister, who found more than 5 per cent, of sulphur in the 
shells of the reptiles, Calotes jubatus, Ptychozoon homalocephalus, and 
Crocodilus biporcatus, concluded that they consisted of a true keratin, 
and the reactions given by the egg-membrane protein of a mono- 
treme, Echidna aculeata, led him to the same conclusion in that case 
also. Table 9 gives the figures which he obtained for the calcium 
and other constituents of some of these egg-shells, as well as the 
very similar investigations of Wicke & Brummerstadt on Alligator 
sclerops. From these fragmentary results, it would seem that the egg- 
membrane protein is here keratin, and a quantity of calcium is 
secreted into the membrane by the animal, varying in amount from 


90 per cent, to 10 per cent,, according to the species. Again, the 
egg-membrane of the Brazihan gastropod studied by RofFo & Correa 
is said, on the basis of qualitative tests only, to be a true keratin, 
containing no reducing sugar and associated with no other sub- 
stances, save 2*45 per cent, of ash. It contained calcium the amount 
of which did not vary during development. 

The transparent horny egg-membrane of the selachian Mustelus ^ 
laevis, which disappears half-way through the development of the ■ 
embryo, has also been investigated by Krukenberg, who compared 
it with the egg-membrane of the grass-snake, Tropidonotus natrix. The 
former resembled the shell-membrane of the hen's egg rather than 
the true keratin of the Myliobatis egg-case. The latter seemed to have 
some of the properties of elastin and some of those of keratin ; from 
it he was able to isolate a reducing carbohydrate as well as glycine, 
tyrosine and leucine. 

Krukenberg was also one of the earliest workers to make quantita- 
tive investigations on this subject. His figures for the protein of the 
egg-shells of Murex trunculatus and the whelk Buccinum undatum, which 
are given in Table 33, led him to make a new class of such substances, 
the conchiolins. As no data exist for the sulphur content of most 
of these proteins, it is impossible to say whether they are keratins 
or not, and the whole subject needs re-investigation. About five years 
later, Engel also investigated the egg-membrane protein of Murex, 
and, obtaining 0-5 per cent, of sulphur from it, concluded, its other 
properties taken into account, that it was a keratin. Engel also agreed 
with Hilger, whose figures for the egg-membrane of the snake, 
Coluber natrix (see Table 30), suggested an elastin as its principal 
component. He had not been able to find any sulphur in it. About 
the same time, Wetzel examined the conchiolin in_the_egg-shells of, 
Mytilus edulis, and obtained from it, after hydrolysis, leucine, tyrosine, 
glycine, Various hexone bases and ammonia, but no phenylalanine. 

The first efforts at quantitative discrimination between egg-mem- 
brane proteins were contented with ascertaining the elementary 
composition ; thus von Fiirth analysed the protein of Loligo vulgaris 
eggs in this way (39 per cent, glucosamine), and Verson, and later 
Tichomirov, decided that the egg-shell of the silkworm, Bombyx mori, 
was a keratin-like body (3-7 per cent, of sulphur), though, owing to 
its unusual properties, they called it chorionin. Of these two last- 
named analyses, it is probable that Tichomirov's is the more accurate. 


for he was more careful to remove all the adhering silk than was 
Verson, and Farkas' independent work agrees rather with his. It is, 
at any rate, clear that the shell-substance of the silkworm's egg is not 
chitin. According to Lavini the inorganic constituents of the silk- 
worm egg-shell are potassium silicate, sulphate, and carbonate, to 
the exclusion of all other salts. 

The work of Pregl and of Buchtala in 1908 is perhaps the most 
thorough investigation of the amino-acid distribution of an egg- 
membrane protein. The figures they obtained are given in Table 
34. The keratin of the egg-case' of Scyllium stellar e was the only 
one of which they made a complete amino-acid analysis ; for that 
of Pristiurus melanostoma and Scyllium canicula they only determined 
the cystine content and large groups such as the monoamino-acid 
nitrogen. Scyllium ovokeratin seemed to follow very closely in its 
constitution the ovokeratin of the hen, according to the figures of 
Abderhalden & Ebstein, which have already been discussed, but 
separated itself off very sharply from it on account of its high tyrosine 
content. The ovokeratin of the tortoise Testudo graeca, which had 
been investigated two years previously by Abderhalden & Strauss, 
was again different, having no tyrosine, but a very high percentage 
of proline. As far as this work goes, it would seem right to con- 
clude that, though the eggs of different species may use similar 
proteins in their external membranes, the constitution of these proteins 
may vary very considerably. 

The work of Steudel & Osato, and of Osato, however, brought a 
new factor into the problem. Their analyses of the egg-membrane 
protein of the herring's egg, which are shown in Tables 34, 38 and 39, 
gave results which differed from the usual keratin figures, but which 
very closely approached the analyses which they were making at 
the same time of the ichthulin of the herring's egg. Thus the amide 
nitrogen (2-05 per cent.) was lower than any of the keratins, but 
approximated instead to the i-8i per cent, of herring ichthulin. What 
appeared to be the case on a general survey turned out to be certainly 
so when the amino-acid distribution was examined, for the two sets 
of figures almost exactly corresponded. The properties of the egg- 
membrane protein and the minute amount of sulphur in it precluded 
its classification as a keratin, and the fact that no reducing sugar 
could be discovered among its breakdown products was convincing 
evidence against its being a mucin. Osato suggested that it was 

Table 34. Distribution of amino-acids in egg-proteins. 

Amide N ... 







Aspartic acid 

Glutamic add 



Cystme ... 

Hiiiudinc ... 


Lysine ... 

Total di-amino 
Total mono-am 
Non-amino N c 

ii Scl 



Present 19'40 — 


4.4 _ ^ 


































50-7 — 






— None 











































6 1 -55 



simply an insoluble modification of ichthulin. As he pointed out, 
industrial use has long been made of insoluble forms of proteins, 
such as casein, and there was no reason why the egg-membranes 
of certain eggs, at any rate, should not be insoluble modifications 
of the proteins of their yolks. Steudel & Osato also suggested that 
the ovomucoid of the egg-white of the hen might be a phylogenetic 
reminiscence of the mucoprotein with which the amphibian egg is 
surrounded. For a review of this work see Steudel. 

The eggs of salps and tunicates are surrounded by a coat of very 
much smaller cells which act as some sort of protection for the 
developing embryo inside. Zavattari has demonstrated histochemi- 
cally the presence of an abundance of glycogen in these test cells, 
and believes that they have a nutritive function. If so, this would 
be a third case where such an active participation of the shell or 
case in embryonic metabolism would have been noted, the two others 
being the abstraction of calcium from the shell of the hen's egg, and 
the contribution of amino-acids by the egg-case of the silkworm. 

A good deal is known about the osmotic and other properties of 
the membranes of amphibian and fish eggs, but these are so intimately 
associated with the physico-chemical processes taking place during 
development that consideration of them will be postponed to Sec- 
tion 5. It will suffice to mention here the experiments of Peyrega, 
who found that the egg-cases of Scyllium canicula were permeable 
to salt. He fitted up osmometers with small pieces of the case as 
the membranes, and observed that it took about 20 days to establish 
osmotic equilibrium with respect to solutions of sodium chloride 
about as strong as sea water, when distilled water was put on the 
other side. These egg-cases have also been shown by Needham & 
Needham to be permeable to urea and ammonia. 

1-13. Proteins and other Nitrogenous Compounds 

The principal protein substance which is found to occur in the 
eggs of all known animals closely resembles the vitellin of the 
hen's egg. It has even been found, according to Chatton, Parat & 
Lvov, in the food-reserves of infusoria. The early analyses of the eggs 
of the pike by Vauquelin in 181 7, of the barbel {Cyprinus barbus) by 
Dulong d'Astafort in 1827, and of the trout [Salmo fario and Cyprinus 
carpio) by Morin in 1823, ^^^ to no more than the view that an 
albuminous substance w£is present in them. But with the work of 


Gobley on the hen's egg, which has already been described, a more 
solid basis for comparison was achieved, and Valenciennes & Fremy, 
in a memoir which received a prize from the Academy of Sciences 
and which was translated into English, proceeded to examine the 
eggs of as many species as were available to them. Gobley's only 
excursion into comparative chemical embryology had been a detailed 
analysis of the carp's egg, published in 1850, but he had not been slow 
to point out the differences between this analysis and that of the hen's 
egg. His figures are shown in Tables 2, 30 and 33, where it will be 
seen that he got a value of 15-76 per cent, protein (wet weight) for 
the hen, and 14-23 per cent, for the carp, but 31-43 per cent, fat 
for the hen and only 2-57 per cent, fat for the carp. The carp's egg 
had, he found, about 10 per cent, more water than the yolk of the 
hen's egg, but only a third of the lipoid substances. 

Fremy & Valenciennes specially directed their attention to the 
protein fraction, and attempted to discover whether the vitellin was 
the same in all eggs. For the most part they relied on histological 
appearances (the "dotterplattchen" were greatly discussed at this 
time), but they also examined the solubility relationships of the 
proteins from each egg, and in some cases subjected the purified 
substances to elementary analysis. The figures they obtained for the 
different compounds are all given in Table 33, and the eggs they 
investigated in Table 35. They were able to isolate a number of 
vitellin-like proteins, soluble in salt solution and precipitated 
by the addition of water. They compared vitellin with fibrin, 
and concluded that the two substances were almost identical, in 
spite of slight differences in the analytical figures — "for bodies 
of this nature", they said, "which are not crystallisable and 
insoluble in water and which are therefore very difficult to purify, 
where is the chemist who could answer for i per cent, of nitrogen in 
an elementary organic analysis?" Ichthin, which they isolated from 
fish eggs, differed from vitellin by not becoming an opaque mass 
when placed for a long time in boiling water, and by giving a 
violet instead of a blue colour when treated with boiling hydrochloric 
acid. Ichthidin, another product offish eggs, differed from ichthin in 
being soluble in water. Ichthulin, the third member of the group, 
differed from the others in not being soluble in all dilutions of saline, 
but in being precipitated from the aqueous extract by further ad- 
dition of water. As for emydin, it closely resembled ichthin, and it is 

SECT. l] 



not easy to see why Valenciennes & Fremy did not identify it with 
that substance. The remaining egg-proteins, which they did not 
further investigate, they referred to under the generic name of 

Table 35. Investigations 

AvES Callus domesticus 


of Valenciennes & Fremy. 



Raia clavata 


Torpedo martnorata 


Scyllium canicula 


Galeus canis 


Alustelus laevis 


Squatina angelus 


Raia fullonica 


Raia rubus 



Cyprinus carpio 

Ichthidin and ichthulin 

Labrax lupus 

Ichthulin and ichthidin 

Alugil chelo 

Scomber scombrus 

Pleuronectes maximus 

Pleuromctes solea 

Solea armorica 

Unidentified species 

of salmon 





Testudo mauritanica 


Cistudo europaea 


Unidentified species 

of lizard 







„ (?) 












Ar-achnida and Insecta — 





Not albumen 

The differences between the compositions which Valenciennes & 
Fremy found for these substances are not great, and it is very doubtful 
whether they are more than modifications of the same substance, 
especially as these workers admittedly had great difficulty in ob- 
taining pure preparations. But the problem of the identity of the 
vitellins is not yet settled. The later investigations are all grouped 
together in Table 33, and the differences between the preparations 
can easily be seen to be small. The work of Plimmer & Scott 
proved that ichthulin is a phosphoprotein closely allied to vitellin. 
Among the more interesting observations must be mentioned 
those of Levene & Mandel; Levene, and Walther, on ichthulic acid 
obtained from the ichthulins of various fish eggs by digestion 


with pepsin and other methods. These with their very high 
phosphorus content approach closely the " paranucleins " or 
vitellic acids obtained from the vitellin of the hen's yolk by 
Levene & Alsberg and others. Evidently there are several possible 
stages of breakdown, for Walther's ichthulic acid only contains 2-8 per 
cent, of phosphorus, while that of Levene has as much as 10-4. 
Here, also, however, there are great variations; thus, while nearly 
all the ichthulins studied have from o-6 to i -9 per cent, of phosphorus, 
the preparation of Steudel & Takahashi from the herring's egg has 
only 0-014 P^r cent. In the yolk of a dogfish egg, Zdarek found no 
less than three proteins, the third of which may possibly correspond 
with Konig & Grossfeld's albumen class. 

In 1908 Alsberg & Clark claimed that phosphorus was quite absent 
from the principal protein of the egg of an ovoviviparous selachian, 
Squalus acanthias, but some twenty years later I re-examined the 
question and obtained without difficulty o-6 per cent, from selachian 
ichthulin (derived from the same species). This yolk also contains a 
second protein, thuichthin, corresponding closely in properties and 
constitution with the ovolivetin of the hen studied by Kay & Marshall 
(see Tables 10 a and 33). 

Gray has studied the properties of the ovoglobulin or ichthulin 
of Salmo fario. If the yolks are poured into water, a dense white clot 
is formed and the water becomes cloudy. The precipitate is soluble, 
however, in acids, alkalies and neutral salts. When the egg-cell 
dies, the egg becomes opaque, and this must certainly be due to the 
precipitation of the globulin, for by placing dead white eggs in 
normal sodium chloride solution they rapidly become clear and 
resemble normal eggs, but regain their opacity when removed to 
distilled water. The clearing process takes 15 minutes but the 
precipitation takes i| hours. Evidently the dead protoplasmic 
membrane can no longer retain in the egg the electrolytes necessary 
for solution of the ichthulin. 

Further work on the properties of teleostean ichthulin was 
done by Runnstrom. 1-5 parts of egg "Pressaft" having been added 
to 1-28 parts of water and the ichthulin precipitated, the effect 
of various ions on its solubility was tried. The anions placed them- 
selves in the order: 

SON > I > NO, > SO. > CI > acetate. 


Thus for 2 c.c. of potassium chloride solution, 0-3 c.c. of distilled 
water had to be added to get coagulation, but to 2 c.c. of KSCN 
solution, as much as 6-4 c.c. The cations went as follows: 

Ca > Mg > Sr > K and Na. 

The egg-white of the dogfish egg was thought by Brande in 1810 
to be identical with the jelly surrounding the egg of the frog, but 
whether the former really consists of mucin and not albumen cannot 
be definitely stated, for no work has since been done on it. However, 
my wife and I, in our work on the eggs oi Scyllium canicula, frequently 
observed a coagulation of the egg-white with acetic acid, which would 
point to the latter possibility. 

The proteins of the echinoderm egg have never been properly 
investigated. Vies, Achard & Prikelmaier have estimated from cata- 
phoresis experiments that the average isoelectric point of the Para- 
centrotus lividus egg-proteins lies between 5-0 and 5-8 pH., but their 
grounds for this figure are not free from criticism. 

Vies & Gex, in some interesting experiments, have studied the 
normal unfertilised sea-urchin's tgg spectrophotometrically. The 
absorption spectrum of the normal egg has peaks or bands at 
wave-lengths of 490, 395, 370, 315, and 230 Angstrom units, and a 
marked trough between 260 and 240 A. This curve is very peculiar, 
for on the one hand it shows much transparency in the ultra-violet 
although most organic substances do not, while on the other hand 
there is nothing at all corresponding to the bands of absorption 
about A 275 which all proteins give. This absorption is brought 
about by the cyclic amino-acids in the protein molecule, and it is 
quite impossible that these should be altogether absent from the 
egg-proteins of the sea-urchin. Vies & Gex considered various 
technical possibilities which might explain these effects, but did 
not think that any of them would account for what was perhaps the 
most remarkable part of the investigation, namely, the finding that 
on cytolysis ("white") a perfectly definite and clear absorption 
spectrum for protein revealed itself In the intact egg, then, this 
must be masked by something else. Speculation on the nature of 
this mechanism would be easy, for all kinds of eflfects might be 
responsible, e.g., formation of complexes, reduction equilibria, and 
satisfaction in vivo but not in vitro of residual valencies in the protein 
molecule. If this very interesting work should lead in the future 


to a revivification in a subtler form of the old biogen molecule 
theory (though it is to be hoped that it will not), not only as regards 
the egg-cell but as regards protoplasm in general, we shall at any 
rate possess in the spectrophotometer a powerful means of studying 
the untouched normal cell-interior. 

Doubt exists with respect to the presence of reducing carbohydrate 
in the ichthulin molecule. Levene & Mandel obtained minimal 
quantities of laevulinic acid from their cod ichthulin, but this 
finding was associated with the presence of purine bases. Six years 
earlier Levene had been unable to find a trace of glucosamine in 
cod ichthulin. Similar negative results were obtained by Steudel & 
Takahashi on herring, and by Hammarsten on perch, ichthulin. 
But the presence of glucosamine in notable amounts has been 
reported for Torpedo ichthulin by Rothera, and for carp ichthulin by 
Walther. While it is possible, and even probable, that ichthulins 
from different fish eggs may vary much, it would be very desirable 
to know to what extent this is the case, and a comparative study 
of ichthulins is much needed. As we have seen Levene & Mori have 
isolated a trisaccharide from avian vitellin. 

Closely allied to the question of the presence of carbohydrate 
groupings in the ichthulin molecule is the equally disputed problem 
of the presence of purine bases in the undeveloped tgg. We have 
already seen that Miescher's identification of nucleoprotein with 
vitellin was quite erroneous, and have described how he was set 
right by Kossel. For the hen's &gg, it is now fairly clear that nucleins 
are present only in exceedingly small amounts at the beginning of 
development, not exceeding, for instance, i or 2 per cent, of the total 
nitrogen or phosphorus. But there has been more difficulty in de- 
ciding what is the real state of affairs in the eggs of fishes and 
aquatic invertebrates. Walther (carp), Hugounenq (herring), Linnert 
(sturgeon), and Hammarsten (perch), all examined the ichthulin of 
these eggs for nucleic acid, and all failed to find the least trace of it. 
Henze, on the other hand, working with the whole tgg of the 
cephalopod. Sepia officinalis, isolated considerable amounts of purines 
together with no less than 1-15 gm. per cent, of a pentose. Tscher- 
norutzki a little later found that 10 per cent, of the total phosphorus 
of the herring's egg could be accounted for as nucleoprotein phos- 
phorus, and the nucleoprotein itself amounted to i-ig gm. per cent, 
dry weight. Masing; Tichomirov, and Needham & Needham reported 


quite similar results with the sea-urchin's egg, the egg of the silkworm 
and the eggs of various Crustacea, echinoderms and an annelid. In 
the sea-urchin egg purine bases were found accounting for 6 per cent, 
of the total nitrogen as nucleoprotein nitrogen, while in the case of 
Bombyx there were 20 mgm. per cent, dry weight. Again, Levene & 
Mandel isolated from their ichthulic acid in 1907 0-344 P^^^ cent, of 
guanine, 0-307 per cent, of adenine, 0-360 per cent, of uracil and 
0-309 per cent, of thymine. Mandel & Levene were also able to 
isolate nucleic acid from cod's eggs. It would certainly appear from 
this evidence as if ichthulin and vitellin may be associated with small 
quantities of nucleic acid. In this connection it is of interest that 
Calvery has evidence that the chick embryo can synthesise "yeast-" 
as well as animal nucleic acid. Steudel & Osato have also obtained 
guanine and adenine from herring's eggs, but this was in the non- 
protein nitrogen fraction, and there was therefore no evidence from 
their work that any preformed nucleic acid was a constituent of the 
egg. The most exhaustive investigation of the problem was that of 
Konig & Grossfeld, who in 1913 set out definitely to clear up the 
discrepancy. As perhaps might have been expected, they found that 
they could isolate purine bases after hydrolysis from all the fish eggs 
they studied, but only in small quantity; their results are shown in 
Table 36. The question of nuclein synthesis by the developing 
embryo will be discussed in relation to these findings in Section I0'3. 

Table 36. Investigations of Konig & Grossfeld. 

Total purine bases isolated 

dry weight 

Cod ... 
Pike ... 

I -060 

But the exact relationship between the nuclein and the vitelHn 
remains exceedingly obscure. It is possible that in one and the 
same egg there may be more than one modification of vitelHn, 
apart altogether from the insoluble form suggested by Steudel & 
Osato. All the knowledge that we possess at the present time 



[PT. Ill 

on this point is of an unsatisfactory histological nature, and any 
discussion of it must inevitably include an unprofitable proportion 
of guesswork. Thus, Jorgensen differentiated histologically between 
two substances which seemed to be present in the unripe egg of 
Patella vulgata, ergastoplasm No. i and ergastoplasm No. 2, one at 
least of which was responsible for the formation of the vitelline 
globules. Faure-Fremiet & Garrault identified ergastoplasm No. i 
with the mitochondria, and ergastoplasm No. 2 with the fatty con- 
stituents of the yolk. But if two forms of vitellin existed, one in loose 
combination with a nuclein and the other free, the staining reactions 
of histological elements mainly constituted by one or other of these 

Table 37. 













and date 








McCrudden (1921) 










A little 
















Levene (1901) 







Walther (1891) 







Hammarsten (1905) 







Valenciennes & 
Fremy (1854) 








Gobley (1850) 

substances would very likely differ, and it is possible that an explana- 
tion on these lines may in the future correlate the chemistry with the 
histology of the yolk. The vitellin question has been in a measure 
reviewed by McCrudden, whose table (given in Table 37) illustrates 
the difficulty of summing up the findings of investigators at all 

The amino-acid analyses (Table 34) are rather more interesting. 
We have data for the vitellins of the herring, the trout, the cod, 
and the sturgeon among fishes, the frog among amphibia, the grass- 
snake among reptiles, and Hemifusus tuba, a gastropod. To this may 
be added amino-acid analyses of the mixed egg-proteins of the sea- 
urchin egg and the eggs of the brook-trout and the giant salamander, 
as well as the albumens of cod and sturgeon and the mucoprotein 
of Hemifusus. If the fish ichthulin analyses of Iguchi or Hugounenq 
be compared with those of Table 1 1 for the vitellin of the hen, no 
very marked differences can be observed, although the predominancy 


of arginine and lysine over histidine, which is a constant feature of 
the ichthulins, reaches greater values in the latter than in the case 
of bird vitellin (see Table 38). Again, bird vitellin always shows 
a notable proportion of proline and leucine, and this is also the case 
with the vitellins of the lower animals (e.g. 10 per cent, of leucine 
in gastropod vitellin, 19 per cent, in snake vitellin and 9 per cent, 
in herring ichthulin), though the amount of proline is usually not so 
great. The only instance of a real divergence between bird and other 
vitellins would appear to be the glutamic acid content, which is 
always high in the former, although this amino-acid is absent from 
the latter. 

Table 38. Hexone bases of yolk-proteins. 

In gm. % original 
In % total nitrogen protein 


Species Protein Hist. Arg. Lysine Hist. Arg. Lysine and date 

Herring Ichthulin 2-45 I4"50 10-07 I'^S 6-33 7-40 Steudel & Takahashi (1923) 

Egg-menibrane 3-99 14-41 7-51 2-09 6-35 5-55 Steudel & Osato (1923) 

Hen Vitellin — — — i-go 7-46 4-81 Osborne & Jones ( 1 909) 

Herring Ichthulin 0-40 2-70 2-00 — — — Hugounenq (1904) 


Sturgeon Ichthulin 0-47 0-97 o-oi — — — Konig & Grossfeld (1913) 

Cod Ichthulin 0-55 0-54 0-02 — — — ,, ,, 

Trout Ichthulin 0-54 0-41 o-oi — — — ,, ,, 

Gastropod Ichthulin None 3-73 0-86 — — — Komori (1926) 

Frog Vitellin 1-14 1-06 0-29 — — — Galimard (1904) 


Snake Vitellin 0-30 0-32 1-45 — — — ,, 

If now Table 39 is considered, it will be seen that variations are 
present in the general analysis of these proteins, but that they tend 
to cancel each other out among the groups. Thus the mono-amino- 
acid/di-amino-acid ratio is very constant indeed in different ichthulins, 
although Rothera himself considered that he was dealing with two 
entirely different proteins, the vitellin of the Torpedo egg and that 
of the sturgeon. It is unfortunate that Komori's examination of 
gastropod vitellin was confined to the estimation of the amino-acids 
by isolation, and did not include a van Slyke determination of the 
relative amounts of mono-amino and di-amino acids. In contra- 
distinction to the ichthulins, the mixed egg-proteins studied by Russo 
and Gortner show more variation, though the former's values for two 
sea-urchin ^gg proteins agree well with the usual vitellin figure. 
Masing, however, was not able to find any phosphoprotein phos- 



[PT. Ill 

phorus in sea-urchin eggs, and Needham & Needham found only 
very little. It is interesting to note that the ratio is subject to large 
fluctuations among the keratins of the egg-cases. As for the albumens 
which Konig & Grossfeld isolated from the eggs of the sturgeon and 
the cod, they seem to approach in their composition, in so far as data 
for the hexone bases permit one to form a conclusion, the ovoal- 
bumen in the hen's egg. The 8 per cent, of tyrosine obtained from the 
sturgeon ovoalbumen is, however, remarkable. The mucoprotein which 
Komori found around the eggs of the gastropod Hemifusus tuba, and 
which he partially analysed, is not sufficiently well characterised to 
be compared except roughly with the mucoprotein of the amphibian 

Table 39. 

In % total nitrogen 


Torpedo {Torpedo marmorata) 


Dogfish (Scyllium stellare) 

„ (Pristiurus melanostoma) 
,, (Scy Ilium caniculd) 


Herring ... 



Giant salamander 





Mixed egg- 
proteins (total) 

Mixed egg-pro- 
teins (coag. only) 

Mixed egg- 

Vitellin (for i 


1 6-43 



849 1-26 6o-20 









and date 

Rothera (1904) 
Buchtala (1908) 

Steudel & Takahashi 

Steudel & Osato 

Russo (1926) 

7-33 2-05 — 62-11 25-91 2-40 

— 284 45-70 17-30 2-64 

— — — 62-20 29-80 209 ,, 

1-82 — — 61-55 28-25 2-18 Gortner (1913) 

2-25 — 
1-63 S-55 

53-73 29-35 1-83 

67-10 25-10 2-67 Plimmer (1908) 

The general distribution of nitrogenous substances in the eggs of 
the lower animals is shown in Tables 40 and 41. Pigorini's investiga- 
tion of the silkworm egg is suggestive, but his data about the 
different protein fractions are insufficient to enable us to form any 
judgment on their relation to those so well known in the bird's egg. 
The very large amount of mucoprotein in the silkworm ovum is 
certainly remarkable. In Table 41 are placed the few data which 
we have on the relative amounts of protein and non-protein nitrogen 
in different eggs, and the way the protein is divided between keratin, 
albumen, and ichthulin or vitellin. Clearly enough there is great 
variation, and a rough dichotomy into two groups, one in which the 


non-protein nitrogen accounts for from 14 to 35 per cent, of the total 
nitrogen, and one in which it only accounts for less than 10 per cent, 
of the total nitrogen. It is evident from the work of Konig & Gross- 
feld that all the fishes examined belong to the first of these categories, 
although within the group there are wide divergences, such as the 
minute amount of albumen apparently present in the trout's egg 
and the low non-protein nitrogen of the herring's egg. Good agree- 
ment is to be noted between the results of Levene and Konig & 
Grossfeld, who all worked on the cod; and, although nothing con- 
cerning the non-protein nitrogen can be gathered from the figures of 
Kensington and Hugounenq, their results do show general agreement 
as regards the partition of nitrogen among the proteins. The only 
reptile on whose eggs work has been done which could be incorporated 
in the table is the grass-snake, and there, although no non-protein 
nitrogen figures are available, it is interesting to note the very high 
proportion of keratin. 

Table 40. 

Silkworm (Bomfryx: mon). (Pigorini, 1Q23.) 
In % of total protein 


Protein sol. in water but not 
Protein sol. in Protein sol. in Protein sol. in coagulable by heat, and 

distilled water 10 °„ salt sol. dilute alkalies yielding glucosamine on 

(albumen) (vitellin) (nucleoprotein) hydrolysis (ovomucoid) 

29-20 8-57 11-45 5090 

The second principal group, consisting of those eggs which have 
a relatively much lower percentage of non-protein nitrogen, contains 
two members, the hen and the silkworm. The former may be said 
with a high degree of probability to be characteristic of all 
nidifugous birds, and perhaps of nidicolous ones also, but whether 
the latter is at all representative of the centrolecithal insect eggs 
may be considered doubtful. The sole insect egg which has been 
investigated chemically, so far, is that of the silkworm, and until 
more evidence is available the hen and the silkworm will have to 
be placed together in this second group without comment. It is 
significant that, in the hen's case, the percentage of albumen is 
greater than in any other, a fact obviously referable to the large 
amount of egg-white present in that egg. Finally, it is of interest 
that the sea-urchin's egg seems to have a protein/non-protein nitrogen 
ratio very like that of the fishes, but situated on the low protein 
edge of their limits of variation. 



Table 41. Distribution of 


% wet 






(by diff.) 


of egg- 
brane Albumen 




bases and 





Carp ... 











































































Sea-urchin (Strongylo- 

centrotus lividus) 


















Grass-snake (Tropido- 

notus natrix) 








Fresh- water gar 











Hen (average results) 

whole egg 
Turtle (Thalassoclielys 

corticata) yolk 











* With so % mucoprotein and 

Within the non-protein nitrogen fraction itself there are some 
fragmentary data for the distribution, as may be seen from Table 42 . 
Unidentified compounds usually account for from 20 to 35 per cent, 
of the total non-protein nitrogen, and free amino-acids for approxi- 
mately half of it. Among those identified by Steudel & Osato were 
histidine, arginine, lysine and cystine. The ammonia may vary from 
4 to 25 per cent., and the purine bases from 15 to 40 per cent. 
As far as can be seen at present, the hen's egg seems to possess 
the greater part of its non-protein nitrogen in the basic fraction. 
The most interesting point brought out by the table is probably the 
significant quantity of urea shown to be present by the analyses of 
Steudel & Osato, amounting to no less than half of the total non- 
protein nitrogen, and it is possible that a good deal of the unidentified 
nitrogen of Konig & Grossfeld might be accounted for in this way. 
The presence of nitrogenous excretory products in the undeveloped 
egg, though at first sight paradoxical, is nevertheless undoubtedly a 
fact in the case of some aquatic organisms. The hen's egg contains 
hardly a trace of urea at the beginning of development but that of 
a selachian fish contains a good deal (see Section 9- 1 1 ) . 


the nitrogen in eggs. 

Gm. % dry weight (ash free) 

^ A . ^ 

% of the total nitrogen Egg- 

, — ^ ■ — \ Pro- mem- Free 

Free tain Pro- brane Nitro- bases and 

Protein Ker- Albu- Ichthu- amino- (N x tein (by pro- Albu- Ichthu- gen amino- Investigate 

total atin men Hn acids 625) diflF.) tein men Hn (direct) acids Fat Ash and date 

66-9 121 548 331 85-37 92-37 1119 50-64 13-65 30-54 7-64 — Konig & Gr 


70-96 11-35 721 52-4 2904 82-75 95-93 10-90 6-92 50-25 13-08 27-87 407 — „ 

85-20 15-7 0-49 790 1485 80-56 89-25 5-10 0-44 70-48 12-89 13-24 IO-7S — 

86-15 12-70 9-15 543 13-9 89-52 85-75 10-88 16-43 46-53 14-33 "-Qi 14-25 — 

68-41 10-50 i-oi 469 315 8933 94-84 9-97 10-48 44-51 14-29 29-88 5-55 — „ 

(loo-o?) — 11-70 880 — 87-80 — — 10-30 77-5 — — 4-50 7-50 Kensington ( 

(loo-o?) 2-7 973 — __ — — — — — — — Hugounenq 

62-0 — — — 379 — _ — — — — — — — Russo (1926) 

94-0 — 27-4 8-05 6-04* — — — — — — — — — Monzini(i9: 

Pigorini (ic 
96-0 — — — 3-98 65-25 — — — — — — — — Russo (1922) 

(loo-o?) 66-0 3-74 30-2 — — — — — — — — — — Galimard (19 

66-0 — — — 33-0 68-09 — — — — — — — — Levene (i89( 

_ ___ — _________ Nelson & Gi 

96-4 406 49-8 42-5 366 — — — — — — — — — — 

Q8-5 — — — 1-5 — — — — — — — — — Tomita (1921 

chorionin in addition. 

As is well known, these fishes have a special relation to this sub- 
stance. In 1858 Stadeler & Frerichs isolated "kolossale Quantitaten 
von Harnstoff" from the organs of plagiostomes, obtaining a solid 
mass of urea nitrate when they added nitric acid to their final con- 
centrates. One liver of an adult Scy Ilium canicula gave them 2 oz. of 
urea, and similar high figures were reported for Acanthias vulgaris. 
Teleostean fishes, however, and the cyclostome, Petromyzon planeri, 
yielded practically no urea, at any rate not more than would be 
present in mammalian tissues. Stadeler confirmed the selachian 
results on Raia batis and clavata and on Torpedo marmorata and ocellata. 
In 1 86 1 Schulze repeated and confirmed Stadeler's work on Torpedo, 
and in 1888 Krukenberg published an extensive work on the subject, 
in which he related his unsuccessful attempts to demonstrate urea 
in the bodies of teleosts {Lophius piscatorius. Conger vulgaris, Acipenser 
sturio), a cyclostome [Petromyzon fluviatilis and Ammocoetes) and a 
cephalochordate (Amphioxus lanceolatus) , although he found large 
amounts of it in the bodies of elasmobranch fishes [Scyllium stellare, 
Mustelus vulgaris and laevis, Acanthias vulgaris, Squatina angelus, Torpedo 
marmorata, Myliobatis aquila) and in the holocephalic Chimaera 


monstrosa. Particularly interesting were his experiments with eggs — 
he isolated considerable amounts of urea from a 5 cm. embryo of 
Mustelus laevis, and from the yolk of Scyllium stellare and Myliobatis 
aquila eggs, but he could find none in the surrounding jelly or "white ". 
An Ggg ofPristis antiquorum yielded 3920 mgm. per cent, (wet weight) 
and a Torpedo ocellata egg 1 740 mgm. per cent. An Acanthias vulgaris 
embryo 1 7 cm. long had 3360 mgm. per cent, in its muscles, 1800 mgm. 
per cent, in its liver, and 2640 mgm. per cent, in its unused yolk. 
Other work on urea in selachians was done by Grehant and by 
Rabuteau & Papillon. 

Table 42. Distribution of non-protein nitrogen in eggs. 

% of total non-protein N (including purine N) 

g-| z § iz g 2 -g I I |Z 

w.« „ „ ^ 2^ c S "G 2 o op Investigator 

Species HSo? cq <fe^ P U D U hUa and date 

Herring — 198 — 44-3 359 — — — — — Konig & Grossfeld (1913) 

Carp ... ... — 39-8 — 36-1 24-1 — — — — — >> >, 

Sturgeon ... — 25-2 13-6 55-4 189 — — — — — ,, ,, 

Herring ... ... 2060 244 67 21-6 — 519 None 18-3 — — Steudel & Osato (1923); 

Steudel & Takahashi (1923) 

Herring 1443 16-91 23-42 41-65 1802 — — — — — Yoshimura (1913) 

Silkworm ... 440 — 4-44 54-30 34-60 — - — — 610 6-7 Russo (1922) 

Hen (aver, figures) — 88-80 4-22 7-04 — None None Trace — — — 

Fresh- water gar 299 92-00 — 4-02 — — — 4-0 — — Nelson & Greene (1921) 

(not ripe) 

More light, however, was thrown on the reasons for this richness 
in urea when in 1897 Bottazzi working on the osmotic pressure offish 
blood, found that the elasmobranchs differed fundamentally from 
teleosts in being isotonic with sea water. 



Selachians Torpedo marmorata —2-26° 

Trygon violacea —2-44° 

Teleosteans Charax pimtazzo —1-04° 

Serranus gigas — i -03° 

Bottazzi observed that the selachian osmotic pressure would corre- 
spond to some 3-9 per cent, sodium chloride but laid no emphasis on 
the fact that selachian blood did not contain anything like so much 
ash. It was left for Rodier to show that the difference was made up 
almost wholly by urea. Duval has since found that the salts alone 
would only give an osmotic pressure of A — i-o6°. "High blood- 
urea", as Smith says, "is a phyletic character of the orders Selachii 


and Batoidei", and its osmotic function was well shown by the 
reciprocal relation between salts and urea which Smith found to 
hold in selachian tissues and fluids. 


mgm. % 

Smith (1929) 


Dogfish {Mustelus canis) 


Denis (1913) 


Dogfish {Mustelus canis) 


Sandshark {Carcharias littoralis)... 


Skate {Raia erinacea) 




Mackerel {Scomber scombrus) 


Goosefish {Lophius piscatorius) ... 


Flounder {Paralichthys dentalus) 


In view of all these facts it is not surprising that Needham & Need- 
ham in 1928 found about 5 mgm. of urea nitrogen present in the 
Scyllium canicula egg at the beginning of development ; and 888 mgm. 
per cent, of urea in the undeveloped Acanthias vulgaris egg. Gori, again, 
found 7 10 mgm. in undeveloped Torpedo eggs. But since urea accumu- 
lation is closely confined to elasmobranchs it is unlikely that the results 
of Steudel & Takahashi and of Konig & Grossfeld can be interpreted 
as being due to urea. 

The presence of urea has also been reported in the undeveloped 
eggs of "ants and flies" (in small quantities) by Fosse. Further 
details would be desirable here. 

There is reason to believe that nitrogenous substances other than 
those already mentioned are present in certain eggs. Thus Yoshimura 
and Poller & Linneweh isolated trimethylamine, tetramethylene- 
diamine and choline from fresh herring eggs, and there is a certain 
probability that fish eggs also contain betaine. As the characteristic 
smell of fish is due to these amines and related substances, this is not 
very surprising. Brieger is said to have found neuridine in fish eggs, 
and Schii eking isolated spermine from echinoderm eggs in 1903. 
Taurine and glycine were found in echinoderm eggs by Kossel & 

Of the manner of formation of ichthulin in the maturation of the 
ovum we know absolutely nothing. Paton & Newbigin concluded 
from a very few analyses that the phosphorus was brought to the 
ovaries from the muscle of the salmon as inorganic phosphorus, but, 
in view of what is now known about the organic phosphorus com- 
pounds of blood, this appears rather unlikely. 


I '14. Fats, Lipoids and Sterols 

Studies on the fatty substances of the undeveloped eggs of different 
animals have resulted in much interesting information. There has 
been, of course, a great body of histological work, and the yolks 
of all kinds of eggs have been repeatedly subjected to microscopic 
examination (for example, Kaneko's study on the silkworm); but, 
in spite of many attempts, I have not succeeded in finding more than 
a few hints in this literature which are of value to the chemical worker. 
This subject has been dealt with in a general way by Ransom and 
by Dubuisson, to whose papers those interested in the histological 
aspects of yolk must be referred. Of the way in which the fat and 
the protein are intermingled in the yolk we know practically nothing, 
and it would be most desirable to investigate the yolk with the 
methods which modern colloidal chemistry has developed. But that 
the association between fat and protein indicated by the histological 
evidence is not very close is shown by the interesting centrifugation 
experiments of McClendon on the amphibian egg. If the egg of the 
frog is centrifuged for five minutes under the right conditions, it 
separates into three perfectly distinct layers, the upper one being 
oily and yellow, the middle one translucent, colourless and proto- 
plasmic, and the lowest one black, containing practically all the yolk. 
By using a considerable number of eggs, McClendon was enabled 
to obtain suflticient material for the chemical analysis of each layer. 
The figures he obtained are shown in Table 43. It is evident from 
a slight inspection of his results that the upper layer is composed 
mainly of neutral fats and a little lecithin, and the middle layer of 
water, salts and protein, with no fats or lipoids. The lowest and much 
the largest layer is made up of the vitellin (ranovin or batrachiolin) 
together with the major part of the lecithin. It is interesting that the 
association between the phosphoprotein and the lipoid was the only 
one that centrifuging could not break, for, as we have already 
seen, the observation of a loose lecitho-vitellin combination in 
the hen's egg is very old. McClendon found that mitotic figures 
were all present in the middle layer, and that this centrifuging 
produced a variety of monstrous embryos. He was led to regard 
the protoplasm of the egg as constant in composition throughout, 
but "anisotropic as regards its axes, in other words crystalline 
in structure". 

SECT. l] 



McClendon extended his observations to the egg of the sea-urchin, 
Arbacia punctulata. Separated by centrifugal force, this egg divided 
itself into four layers, as Lyon had already described, {a) a layer of 
yolk bodies and red pigment granules extending from the centrifugal 
end about half-way to the equator, {b) a layer of similar yolk bodies 
but without the pigment granules, {c) a translucent fluid layer ex- 
tending almost to the centripetal pole and containing the nucleus, 
and finally {d) a very opaque layer or cap of minute volume, sitting 
on the centripetal pole. When the crushed eggs were centrifuged, 
the material separated into two layers, {a) and {b) being indistin- 
guishable, centrifugal and containing the egg-membranes, and 
[c) centripetal, {d) not being perceptible. McClendon analysed the 
layers in the same manner as those of the frog's egg — the figures 
are given in Table 43. 

Table 43. 
McClendon' s figures (1909). 




in the layers 


, of 







dry weight 







t! 2 

c t< 

—1 1) 


*-> tJ 

& 2 


Layers of centri- 



Upper centripetal 












fuged egg of 

(fatty or oily) 

Rana pipiens 



Middle (proto- 















Lower centrifugal 













Layers of centri- 



Centripetal (proto- 













fuged egg of ^r- 


bacia punctulata 



Centrifugal (yolky) 













A short consideration of them shows that centrifugal force is not 
nearly so successful in separating the egg of the sea-urchin into 
chemically unlike layers as it is in the case of the frog. This fits in 
perhaps with the long-established fact that centrifugal force inter- 
feres far less with normal development in the sea-urchin's egg than 
it does in the frog's egg (Morgan and Lyon). It was very noticeable 
that, whereas the frog's egg separated out into layers of markedly 
different water-content, this did not take place in the sea-urchin's 
egg. In the case of the centrifuged frog's egg, again, there were big 
differences between the phosphorus contents of the different layers, 
but in that of the sea-urchin's egg this only applied to the residues 
which were mainly protein. McClendon surmised that the inclusion 


of the membrane proteins in the centrifugal layer caused this 

It is of course a fact of the first importance that normal develop- 
ment can follow centrifugation and this will receive attention later 
(see Section 3 and the Epilegomena) . I shall only mention here 
as one of the best instances of this phenomenon, the work of 
Schaxel on the axolotl egg. Here centrifugation caused atypical 
discoidal cleavage which nevertheless resulted in a normally pro- 
portioned embryo. Thus normal conclusions can follow abnormal 
distribution of the so-called "organ-forming substances". For further 
details of these experiments, see Morgan and Bertalanffy. 

The early work of Gobley on the fat of the hen's and the carp's 
egg has already been described. He isolated glycerophosphoric acid 
from the latter, and pursued further his investigation of lecithin, 
concerning which it is of interest to note that Sacc contested his claim 
to have found organic alcohol-soluble phosphorus. Sacc believed 
that the fats contained dissolved in them a quantity of inorganic 
phosphorus. Gobley, however, was easily able to disprove this view 
and to show the identity of carp's egg lecithin with brain lecithin. 
Data which have accumulated since Gobley's time on the fatty 
substances of the eggs of the lower animals are collected in Table 44, 
and may be compared with those in Table 22. One of the most 
striking differences between the hen's egg and other eggs is the 
relatively low iodine value of the fatty acids of the former, both free 
and combined in lipoids. The neutral fat of the hen's egg has an 
iodine value varying roughly between 60 and 90, but for fish eggs 
the figures vary from 90 to 150, and the same rule holds generally 
of the lipoid fatty acids, for they average 60 in hen and 100 in 
fish eggs. The saponification numbers, on the other hand, are much 
the same throughout the two tables (from 170 to 200). The conclusion 
might therefore be drawn that egg fats differ rather more as to the 
number of unsaturated linkages in their acids, than as to the length 
of their chains. Nevertheless, there are remarkable exceptions to 
these generalities, the fatty acids of the echinoderm eggs, for example, 
having enormous saponification and high Dyer numbers, and there- 
fore presumably only very short chains of carbon atoms. Arbacia 
is more remarkable in this than Asterias. Yet, though they are 
exceptional in that respect, they have iodine numbers very like those 
of fish-egg fats. Another point of interest is that the cholesterol/fatty 





acid ratio, as shown by expressing the cholesterol in percentage of 
the fat present, is rather constant, never going below 4 and never 
rising above 12. This may have some connection with the physical 

Table 44. Data for fat fraction of eggs. 


"o-tio a 











C a 

?f H ^ 5 






- c 



Qj cj.S .2 

■3 c 






.-a (u u 

— 2 

J5 4^ 




3 u 




^ ^ 

m c 

Q^Z c 







and date 


Frog {Rana tempor- 










Faure-Fremiet & Dragoiu 




Sturgeon ... 










Konig & Grossfeld (191 3) 











„ ,, 



1 76- 1 








,, jj 

Herring ... 









,, J, 











55 55 











55 3J 

Trout {Salmo fario) 










Faure-Fremiet & Gar- 



Fatty acids of the ph 

osphatide fraction' 

rault (1922) 

Carp {Cyprinus carpio) 



■ — 







55 55 



Fatty acids of the phosphatide fraction' 




Fatty acids of the phosphatide fraction^ 

Ponce (1924) 

Shark (Lepidorhinus 










Tsujimoto (1920) 



Sea-urchin {Arbacia 










Page (1927) 


Sea-urchin [Echinus 










Moore, Whitley & Adams 




Fatty acids of the phosphatide fraction] 


Sea-urchin {Arbacia 










Matthews (191 3) 


Sea-urchin [Paracen- 










Ephrussi & Rapkine 

trotus lividus) 


Starfish (Asteriasgla- 










Page (1927) 



Polychaete worm 










Faure-Fremiet (1921) 

{Sabellaria alveolata) 


Roundworm {Ascaris 










Faure-Fremiet (191 3) 


State of the egg-cell, and will be referred to again (see Section 12-5). 
The lipoids, expressed as lecithin in per cent, of the fat present, show 
greater variations, but it is not possible to say at present what the 
significance of these may be. 


The mention of squalene in Table 44 indicates the existence of an 
egg-constituent, our knowledge of which is of very recent origin. In 
1 906 Tsujimoto isolated from the liver oils of elasmobranch fishes a 
saturated hydrocarbon of approximate formula C30H20, and in 191 6 
published a further study of it. Its properties and constants are given 
in Table 22. In 1920 he reported that he had been able to isolate 
it from the egg-yolks of two elasmobranchs, Chlamydoselachus anguineus 
and Lepidorhinus kinbei, where it made up no less than 13 per cent, 
of the egg (wet weight) and, in another case, 1 7 per cent, at least of 
the total fat fraction. There the matter rested until 1926, when 
Heilbron, Kamm & Owens, taking up the question of its presence 
in eggs once more, isolated it from the undeveloped yolks of Etmo- 
pterus spinax, Lepidorhinus squamosus and Scymnorhinus lichia. In the 
fully developed eggs of the first-named of these three, practically 
none was present, indicating that it must either have been combusted 
or absorbed during development. Further researches on the embryo- 
logical significance of this compound are greatly required. It is 
possible that some hydrocarbon of this sort may explain certain 
obscure points in the chemistry of the egg, for instance, the oil 
extracted by Dubois from the locust's egg {Acridium peregrinum). It 
contained 1-92 per cent, phosphorus, and was present to the extent 
of 4*5 per cent, of the wet weight of the egg, no small proportion. 
Kedzie studied a similar oil which he obtained from the egg of the 
American locust. 

A question which is perhaps related to the general problem of the 
egg-oils is that of the oil-globules of the yolks of some of the teleostean 
fishes. In 1885 Agassiz & Whitman divided all pelagic eggs into 
those which had the oil-globule and those which had not. But it 
was soon found that this method of classification was valueless, for 
the appearance of the globule is rather erratic; thus, although Lota 
vulgaris (van 'S>2ivs\he\ie) , Brosmius (anon.) and Motella mustela (Brook) 
were all found to have it, the common pike's egg does not have it 
(Truman). Ryder first suggested that the oil-globule might have a 
relation to buoyancy, but Prince, reviewing the whole subject a little 
later, pointed out that this could hardly be so, for the salmonoid 
fishes all have them, and yet their eggs never float. Moreover, out 
of 22 teleost eggs with no globule, 17 are pelagic, while out of 
24 teleost eggs which have globules, only 15 are pelagic. Ryder 
replied to this by partially withdrawing his theory, and Mcintosh 


simultaneously showed that the eggs of the catfish, which are un- 
doubtedly bottom ova, have large oil-globules. Another theory was 
put forward by van Bambeke, who believed that the oil-globule was 
a special form of yolk, and of a purely nutritional significance. Prince 
criticised this view on the ground that the oil persists in the yolk 
after the liberation of the embryo from the egg-membrane, and travels 
beneath it as it swims about. This would not, however, negative the 
possibility that the oil was used for larval rather than embryonic 
nourishment. Van Bambeke' s claim that a protoplasmic thread 
passes from the oil-globule to the germinal disc was almost completely 
disproved by van Beneden. His and Miescher, examining the oil 
histochemically, found that it only stained very slowly with osmic 
acid, and therefore differed profoundly from the yolk, and, although 
it was soluble in ether, it contained no more than a trace of phos- 
phorus. It is remarkable that the oil has never been subjected to 
a proper chemical examination, especially in view of the extensive 
zoological literature on it. What we know of its properties faintly 
hints, perhaps, that it may be a hydrocarbon like squalene, and the 
whole question, indeed, holds out great possibilities for physiological 
as well as chemical work. The oil must readily dissolve lipochromes, 
for the pink pigment of the salmonoids is found in it. Prince's own 
theory was that the globule was a constituent of ancestral significance, 
a vestige from the time when, as Balfour showed, the teleostean yolk was 
very much larger than it is now. The nutrition view is probably the best. 
The lipoids and sterols of the eggs of the lower animals are very 
little known, and their further study is much to be desired. Page in 
1923 described a sterol — asteriasterol — which he isolated from the 
eggs of Asterias forbesii and which turned out to be closely related to, 
though not identical with, ordinary- cholesterol; the eggs of Arenicola 
cristata, on the contrary, yielded a sterol absolutely identical with 
the well-known substance as it occurs in mammals. Ten years pre- 
viously, in a less accurate study, Matthews had failed to find any 
cholesterol at all in the eggs of Asterias forbesii, though he had been 
able to isolate some from those of Arbacia punctata. From the former 
he got a jecorin-like substance, containing 10 per cent, of glucos- 
amine, which was probably a mixture of kephalin, cerebrosides, 
"protagon" and various carbohydrates. Page's later study of the 
fats and lipoids of the echinoderm egg led to the conclusion that 
(qualitatively) there was more kephalin in the eggs of Arbacia than 


in those of Asterias, and more lecithin in the eggs of Asterias than 
in those of Arbacia. Asterias contains large amounts of soaps, and 
its oil is present in much greater abundance than the oil of 
Arbacia; moreover, it contains more sulphur compounds (sul- 
phatides?) decomposable with potash than does the Arbacia egg. 
Page, Chambers & Clowes made a study of the effects of various 
cytolytic agents on the eggs of Asterias separated by microdissection 
into their cortical and endoplasmic components. They used for this 
purpose hypotonic sea water, digitonin and saponin, and found that 
digitonin caused slow cytolysis of the cortical and rapid cytolysis of 
the interior protoplasm when the two were isolated, whereas hypo- 
tonic sea water caused slow cytolysis of the interior and rapid 
cytolysis of the cortical protoplasm. If these results do not actually 
demonstrate that the greater part of the asteriasterol is localised in 
the outer and fertilisable parts of the egg, they at any rate suggest 
a new method of investigation which may help to solve many similar 
questions in the future. Runnstrom has studied the lipoids of the 
echinoderm Qgg in relation to its coloured interference fringes and 
its membrane properties. 

Among the sterols existing in eggs must be mentioned a substance 
which has long been known to occur in the ova of Ascaris, and which 
has been called "ascarylic acid". Faure-Fremiet identifies it with 
the droplets or crystals described in the egg oiAscaris by van Beneden. 
It was isolated simultaneously by Faure-Fremiet from the eggs and 
by Flury from the whole body of the nematode ; the former worker 
found that it accounted for 22 per cent, of the dry material. Ascarylic 
alcohol, ascarylic acid, or, as it would probably be best to call it, 
ascaristerol, seems to exist in the egg-protoplasm in combination 
with palmitic, oleic, and perhaps stearic acid in ester form. Faure- 
Fremiet & Leroux studied its properties, and proposed the pro- 
visional formula of C32Hg404 . Its saponification number was 199, and 
its m.p. 82°, it did not give the cholesterol colour-reactions, and its 
molecular weight was close to 511. Flury considered it to be related 
to oenocarpol. Acaristerol seems to be strictly confined to the eggs, 
for even the parietal cells of the ovary and uterus do not contain it, 
as Faure-Fremiet showed by means of histochemical tests. Nor is it 
present in the testes and spermatozoa. It may at present be classed 
with the sterols, like asteriasterol. Ascaris eggs also contain o-i6 per 
cent, dry weight of ordinary cholesterol. 

SECT. l] 



Table 45. Distribution of phosphorus. 

In % of the total P 









15 p-^ 




^ U 

^ JJ 

. w 







3 fl 

2 G 








7 -S 


and date 










Plimmer & Scott (1909) 


Frog (ovarian) 








Plimmer & Kaya (1909) 










Plimmer & Scott (1908) 








■>■) J3 

Grey mullet 








5» J> 









Faure-Fremiet & Garrault 









Yoshimura (191 3) 








Milroy (1898) 









Tschernorutzki (191 2) 









Paton (1898) 







Steudel & Takahashi (1923) 


Sea-urchin {Strongylo- 








Robertson & Wasteneys 

centrotus purpuratus) 


Sea-urchin {Arbacia 








Masing (1910) 


Sea-urchin [Arbacia 








McClendon (1909) 


Sand-dollar {Dendras- 








Needham & Needham ( 1 930) 

ter excentricus) 

Starfish {Patiria mini- 








J> 59 



Sand-crab (Emerita 


6 1 -40 






>J J> 


Brine-shrimp [Artemia 








)> >5 

Gephyrean worm ( Ure- 
chis caupo) 





15-80 Trace 


5> J) 

Roundworm {Ascaris) 








Faure-Fremiet (191 3) 

Miescher (1872) reported that in the salmon nearly all the phosphorus is in organic form. 
* This fraction will include pyrophosphate P. 

t This fraction will include guanidine phosphoric acids (arginine or creatine phosphate P). 
+ "Present in some quantity." 

The lipoids of the mammalian egg-cell have recently been the 
subject of some work which is interesting, though, Uke all histo- 
chemical studies, very difficult to appraise. Following on Russo's 
claim to have found two different sorts of eggs in rabbits, varying 

N E I 23 


in their reactions to staining methods, Fels in 1926 confirmed this 
difference for the human egg-cell, some specimens of which showed 
a strong lipoid-reaction (Ciaccio and Smith-Dietrich methods) in the 
nucleolus while others did not. Fels' illustration is certainly striking. 
Leupold had already put forward the view that eggs whose nucleoli 
were rich in lipoids produced females, and the remainder males, but 
all the evidence, however, is against sex-dimorphism in the mam- 
malian egg (see Parkes' review). These observations, together with 
those of Pollak on the presence of Reinke's crystals in the egg of 
Macacus rhesus, and similar work by Limon and" von Ebner (on 
Cerrus capreolus), are all that we have on the chemical constitution 
of the mammalian egg-cell. 

Closely connected with the lipoids of the egg is the distribution 
of phosphorus compounds in it and Table 45 gives what is known 
upon this subject. It is interesting to see how the phosphoprotein 
phosphorus varies, in some eggs being very large in proportion to 
the total phosphorus, in others being almost insignificant. Masing 
was wrong in saying that the echinoderm egg has none at all, for 
Needham & Needham in 1929 observed quite a high percentage 
in the &gg of the sand-dollar. It is significant in view of what 
has already been said about the pre-eminence of birds in storing 
fat in their eggs, that the hen's egg has 20 per cent, more 
phosphorus in lipoidal form than any other egg investigated. 
The fishes rank in this respect with the echinoderms and annelids, 
little diflference being noticeable between alecithic and lecithic eggs. 
Perhaps this famous distinction involves neutral fat rather than 

It is to be noted from Table 45 that the inorganic phosphorus 
content of eggs is very variable; in many cases almost none is present, 
but the haddock's ^gg seems to have no less than 20 per cent, of the 
total phosphorus in this form. About the same proportion is present 
in the nematode egg, ii Ascaris can be taken as representative. Faure- 
Fremiet was able to identify the calcium phosphate in the egg-cyto- 
plasm with the "hyaline balls" described by van Beneden, using 
various histochemical reactions (McCallum, Prenant, etc.). Pure 
calcium phosphate, according to Faure-Fremiet, accounts for 0-4 to 
0-6 per cent, of the dry weight of Ascaris eggs, an inconsiderable 
amount in view of the share it takes in the appearance of the cyto- 
plasm as a whole. 


1-15. Carbohydrates 

The carbohydrates of the eggs of the lower animals have been less 
investigated than anything else — a summary of our quantitative 
knowledge concerning them is shown in Table 46. The presence of 
glycogen in insect and mollusc eggs was noted by Bernard and in 
those of arachnids by Balbiani. For the reasons mentioned above, 
it is difficult to know how trustworthy the figures for carbohydrates 
are, so bad have the methods been in the past. Faure-Fremiet & du 
Streel's figure for the glycogen of the frog's tgg must surely be too 
high, for most of the other workers are agreed on a value of about 
2 gm. per cent, wet weight. In the case of animals other than 
amphibia, the figures are too scattered to permit of any generaUsa- 
tion: thus, though glycogen was not found in herring's eggs by 
Steudel & Osato, Gori did note its presence in Torpedo eggs, and the 
eggs of the reptiles Vipera aspis and Elaphis quadrilineatus, in addition 
to free carbohydrate. Steudel & Osato pointed out that many histo- 
logists such as Goldmann had published results concerning the fish 
egg which might lead one to suppose that very large amounts of 
glycogen were there. That this was not found by chemical methods 
ought to induce, they felt, a more cautious attitude towards histo- 
chemical work than was customary; indeed, much of what is called 
glycogen histochemically can certainly not be glycogen. Greene's 
carbohydrate figures for the eggs of the king-salmon Oncorhynchus 
tschawytscha, from Cahfornian rixers, were of special interest, for, 
throughout the maturation period, the carbohydrate content of the 
egg remained the same. The duration of the fast did not affect it 
at all. 

Quahtative investigations of carbohydrate in eggs have been made 
by Anderlini on the silkworm egg and by Konopacki, who observed 
the presence of glycogen microchemically in the perivitelline fluid 
of the frog's tgg. As has already been mentioned, a carbohydrate 
group is undoubtedly contained in the mucoprotein of the amphibian 
egg-jelly, and von Furth's analysis of the egg-cases of the squid Loligo 
vulgaris showed that their protein also contained a carbohydrate, but 
whether these play any part in the sugar supply for the developing 
embryo remains an obscure point. Haensel found an amount of glucose 
in the frog's tgg which is shown in Table 46, but he also tried the effect 
of keeping the eggs in solutions of various mono- and di-saccharides, 




[PT. Ill 

Table 46. 

Mgm. % wet weight Mgm, % dry weight 

. ' , , ' ^ 

6 ^ 4 ^ 

% y ^ h y c 

S-o iJ ^ l-S.^ >■ Investigator 

Species H-c'fa O h-o^ta O ^nd date 

Turtle ( Thalassochelys corticata) 

White ... ... ... — Trace — — — — Tomita (1929) 

Yolk ... ... ... — 100 — — — — ,, 

Tortoise {Testudo graeca) ... — 140 — — — — Diamare (1910) 


Frog {Rana esc. and fuse.) ... — — 2,520 — — — Kato (1909) 

,, ,, ... — — 1,100 — — — Athanasiu (1899) 

Frog {Rana temp.) ... ... — — — — — 7810 Faure-Fremiet & 

Dragoiu (1923) 

Frog {Rana esc. and fuse.) ... — — 2,500 — — — Bleibtreu (1910) 

Frog {Rana temp.) ... ... — — — — 193 — Gori (1920) 

,, ,, ... ... — — 10,140 — — — P'aure-Fremiet & Vivier 

du Streel (1921) 

„ ,, ... ... 604 — — 1906 — — Needham (1927) 

,, ,, ... ... — — 2,528 — — — Haensel (1908) 

,, ,, ... ... — — 1,650 — — — Goldfederova (1925) 


Herring — 500 — — — — Steudel & Osato (1923) 

King-salmon {Oncorhynchus — 96 — — — — Greene (1921) 


Trout {Salmo fario) ... ... — — 340 — — — Faure-Fremiet & 

Garrault (1922) 


Starfish {Asterias glacialis) ... — — 20 — — — Dalcq (1923) 

Sea-urchin {Echinus esculentus) — — i ,360 — — 8980 Moore, Whitley & 

Adams (1913) 

Sea-urchin {Strongyloeentrotus 1360 — — 543° — — Ephrussi & Rapkine 

lividus) (1928) 


Silkworm {Bombyx mori) ... — — 1,110 — — — Pigorini (1922) 

,, ,, ... — — 1,980 — — — Tichomirov (1882) 

), „ ... — — — — — 3080 Vaney & Conte (1911) 

Bee {Apis mellijica) ... ... — — 2,500 — — — Straus (191 o) 


Octopus {Sepia officinalis) ... — — None 3620 1000 None Henze (1908) 

,, As glucose ... ... 2700 — — — — — ,, 

,, As pentose ... ... 2380 — — — — — ,, 


Polychaete worm (^aie/Zana — — 1,270 — — — Faure-Fremiet (192 1) 


Roundworm {Ascaris megalo- — — — — — 2105 Faure-Fremiet (1913) 

Table 47. Ash content of eggs. 



Pike (£j« lueiw 


Sturgeon [Acitie 
Sea-urdiilt [Arb 


Starfuli LUUtia. 

Sea water (Wo 

ih Hole) 

Sea waier {Clia 

tnga cxpcdilion) 

Sea- urchin (Sir 

neylQcentrolus lividtu) 

Dogfish {^p'""' 
Spider-crab (A/ 

, cmicula) ... 

no vtTTUCOsa) ... 

Octopiu tStpia 


Hen (6'<i//uj Join 

'»""")■■• - 

MotluK ( Volula 
Dogfuh {Squaiin otonllUas) 
Frog {Rana Umporaria) 
l-rout (&ilmo fontimlii) 
Salmon {Saimo ndar) ... 
Wrauc (Labrax lupus) ... 
Torpedo [Torptdo dctllala) 
Dogfiah [Snilium canicula) 
Spidcr-aab {Maia vnrucosi 
Octopu) (Stpta ojficinalij) 

a pmtuloia) 

Gephyrcon worm {Sipuncutus nitdui) . 
Lugworm [.irtnitola claparti"" 
Herring {Glupea hariagus) 


Salmon .. 


Dogfuh \Squatut acanthiai) (cgg-jclly) 
Sawfish {Pritlii aniiquorum) 

Mtlhi:quivalcnLa prcx 

SO, PO, a 

— 55- 

Na Mg Ca 



413 < 






300 10 


I -05 





46-6 - 5 




1-04 16-29 ^fj^ ■6'65 ■iS-29 
3-9B g-6i 11-51 1707 ^bs 
— 10-79 ^3^ 4<'85 

;&.Grossreld(i9i3) 2-08 

'■«<> Page (1927) 

a-27 — ■ O4-0 7S-3i 409 ia-37 „ 

0-004 5'-7 45-^2 Si-s^ 54*42 57-'i 

— 4-64 — 34-a 54-03 

47 b'^'b'^ 5^'^ Diiunar, ualUnger, vol. 1 
■64 13-44 9"3i I3'5i Goblcy {1850) 
- — — — Wetzel (1907) 

— — 33-7 

t' z 'U *;? 

■54 — afj-g 

— 3'-9 — 

'"3 — 559 

5 — — 

7a — — 











6 — — 

Silkworm iBombyx n 

Turtle [Timloiiochew coTticata): 

Whole egg 



>9'03 30-S8 Btalasccwicz (1926} 
6i-oi 63ja RoBb & Correa (1927) 

McCailum (1926) 

Greig {1898) 
Milroy [1898) 
Perugitt (1879) 
KrukeabcTS (1888} 


Hen {Callus domaliats) 

Frog {Rana lembotana) 

Trout {Salmo/ontinatis) 
Torpedo {Torptdo ocillata) 
Spiaer-crab ^oifl wrrwfwfl) ... 
— Sea-urchin (raracentntus lividus) 
Octoput [Stpia qfficimlii) 

Schroder (1909} 
Karaahima (igag) 

i?-j Bialasccwiti (i< 


to see if they would grow richer in glycogen. They all did; in fact, 
he was able to double their glycogen content by this simple means 
(glucose acted better than sucrose, sucrose than lactose, and lactose 
than glycerol, though even the latter substance gave an effect) . These 
curious observations have never been confirmed, and can hardly be 
said to carry conviction as they stand. Diamare obtained discordant 
results in his researches on the sugar of various eggs ; thus, he got a 
rather low value for the free glucose of the egg of Testudo graeca, but 
none at all, either free or combined, from the eggs of Scyllium catulus 
or Torpedo marmorata. No explanation can be given for this fact. In 
connection with carbohydrates, it should be remembered that viper 
venom, which is in all probability a glucoside, has been shown by 
Phisalix to be present in active form in the yolks of viper eggs. 

I -16. Ash 

We come now to the inorganic substances of eggs. Iron has been 
shown to be present by microchemical tests in many eggs, such 
as those of Limnaea, Tubifex, Rana esculenta (where it is massed 
at the light ventral pole) and Pisidium, by the work of Schneider. 
Dhere found traces of iron and copper in the eggs of Sepia. Warburg 
found 0-02 to 0-03 mgm. iron per 100 mg. nitrogen in the unfertilised 
sea-urchin €:gg', part of it seemed to be in ionic form and part not. 
According to Wilke-Dorfurt, there are 4-8 mgm. per kilo iodine in 
oyster egg-shells. 

Ash analyses of eggs have been made by several workers, whose 
results, it may be remarked, would have been more easily comparable 
if they had expressed them in the same way, instead of in nine or 
ten different ways, omitting in some cases the figures which would 
enable them to be calculated into a form comparable with each 
other. Table 47 summarises what is known about the distribution 
of inorganic substances in eggs. It has entailed a good deal of calcula- 
tion, for only one of the previous investigators expressed his results 
in terms of millimols and milliequivalents, and unless this is done it 
is impossible to gain any idea as to the relative preponderance of 
cation and anion. The first thing which should be noted is the 
fact that, when the salts are expressed in per cent, of the total 
ash, potassium is always there in greater amount than sodium, and 
nearly always to a greater extent than any other metal. This seems 
to be quite characteristic of the ovum, though in other systems of 


to see if they would grow richer in glycogen. They all did; in fact, 
he was able to double their glycogen content by this simple means 
(glucose acted better than sucrose, sucrose than lactose, and lactose 
than glycerol, though even the latter substance gave an effect) . These 
curious observations have never been confirmed, and can hardly be 
said to carry conviction as they stand. Diamare obtained discordant 
results in his researches on the sugar of various eggs ; thus, he got a 
rather low value for the free glucose of the egg of Testudo graeca, but 
none at all, either free or combined, from the eggs of Scyllium catulus 
or Torpedo marmorata. No explanation can be given for this fact. In 
connection with carbohydrates, it should be remembered that viper 
venom, which is in all probability a glucoside, has been shown by 
Phisalix to be present in active form in the yolks of viper eggs. 

i-i6. Ash 

We come now to the inorganic substances of eggs. Iron has been 
shown to be present by microchemical tests in many eggs, such 
as those of Limnaea, Tubifex, Rana esculenta (where it is massed 
at the Ught ventral pole) and Pisidium, by the work of Schneider. 
Dhere found traces of iron and copper in the eggs of Sepia. Warburg 
found 0-02 to 0-03 mgm. iron per 100 mg. nitrogen in the unfertiUsed 
sea-urchin egg ; part of it seemed to be in ionic form and part not. 
According to Wilke-Dorfurt, there are 4-8 mgm. per kilo iodine in 
oyster egg-shells. 

Ash analyses of eggs have been made by several workers, whose 
results, it may be remarked, would have been more easily comparable 
if they had expressed them in the same way, instead of in nine or 
ten different ways, omitting in some cases the figures which would 
enable them to be calculated into a form comparable with each 
other. Table 47 summarises what is known about the distribution 
of inorganic substances in eggs. It has entailed a good deal of calcula- 
tion, for only one of the previous investigators expressed his results 
in terms of millimols and milliequivalents, and unless this is done it 
is impossible to gain any idea as to the relative preponderance of 
cation and anion. The first thing which should be noted is the 
fact that, when the salts are expressed in per cent, of the total 
ash, potassium is always there in greater amount than sodium, and 
nearly always to a greater extent than any other metal. This seems 
to be quite characteristic of the ovum, though in other systems of 


the organism other relations are found; thus corpuscles and plasma 
of some mammalian bloods have converse potassium/sodium ratios, 
and, as a general rule, potassium preponderates in cells while sodium 
preponderates in media. Of the anions PO4 usually takes up much 
the greatest part, but SO4 may in certain cases equal it. In the 
columns on the right of the table the total anion and total cation 
are shown, in each case calculated as millimols and as milli- 
equivalents, the former giving an idea of the total number of 
molecules present, the latter of the total number of valencies. 
Study of the anion/cation ratio expressed as milliequivalents per 
cent, wet weight provides an important key to the constitution 
of the egg, for it shows roughly to what extent anion or cation is 
held in combination with protein or lipoid, or other organic sub- 
stances. We have already seen that in the case of the hen's egg, 
taking both yolk and white into account, the anion/cation ratio is 
more than unity (Bialascewicz's figures give 2-17), showing that a 
quantity of sulphur and phosphorus is in organic combination — a 
conclusion which fits in admirably with all that we know of the 
hen's egg from other sources. The same relationship is seen in the 
figures of Konig & Grossfeld for the three fish eggs they investigated, 
the pike, the cod and the sturgeon. On the other hand, the figures 
of Page for two echinoderm eggs give ratios much less than unity, 
demonstrating the organic combination of a good deal of the cation. 
It may be noticed that the analyses of Dittmar and Page for sea 
water give ratios in the very close neighbourhood of unity, as would 
be expected, and indicate at the same time that the ratio cannot be 
regarded as significant to less than o-og. From what has been said, 
therefore, it might be concluded that the yolk-laden eggs of the 
fishes, like that of the hen, have a ratio above unity, while the 
alecithic echinoderm eggs have ratios much below it. But there 
are exceptions to this generalisation. The ratio of unity for the 
carp egg which is given by Gobley's results may perhaps be 
neglected, owing to the date of the work (1850), and the similar 
value obtained by Roffo & Correa on a gastropod egg may 
also be regarded as suspicious because of the enormous amount of 
sodium chloride that appears in their analysis. But the careful work 
of Bialascewicz in 1926 does not altogether support the generalisa- 
tion. His figures for the fish egg are in good agreement with those of 
Konig and Grossfeld, but his anion/cation ratios for the echinoderms 


do not go below unity, though they approach it much more nearly 
than do the fishes. Further work is needed to clear up this contra- 
diction. In one case, however, Bialascewicz got a ratio below unity, 
that of Arenicola claparedii, so that in a general sense his investigations 
are not opposed to those of Page and Konig & Grossfeld. McCallum's 
low ratio for the egg of the herring is difficult to explain, but 
Perugia's analysis of the egg-jelly of ovo viviparous selachians fits in 
well enough with the majority of the other evidence. Attention might 
also be drawn to Bialascewicz's high ratio (15) for the eggs of the 
octopus. Sepia, which would appear to be extraordinarily poor in 
metallic ions (cf. p. 317, Section 13 and the Epilegomena). 

Some further light is perhaps thrown on the inorganic composition 
of eggs by Wetzel's figures for insoluble and soluble ash. He sub- 
mitted the eggs of various animals to examination, with the following 
results : 

% dry weight 

Species Total ash Insol. ash Sol. ash 

Sea-urchin {Strongylocentrotus lividus) ... 9-7 2-4 7-2 

S^iideT-cvah {Maia squinado) ... ... 4-12 0-27 3-8 

Octopus {Sepia officinalis) ... ... ... 2-2 0'59 i'6 

Tio^sh. [Scyllium canicula) ... ... ... 5-5 1-15 4-3 

In all cases he found more soluble than insoluble salts, i.e., more 
chlorides than sulphates and phosphates. 

Table 48. Bialascewicz' s figures. 


Vol. of 


Vol. of 


CI in I c.c. 

Total CI 


c.c. of 




in ultra- 







fluid per 







I c.c. yolk 

Hen (yolk) 




I -08 






























It is very interesting, as Bialascewicz points out, that the mineral 
composition of terrestrial and aquatic animals should be so alike. 
The preponderance of potassium which is seen in the hen's tg^ does 
not change as one passes to organisms laying their eggs in an environ- 
ment containing far more sodium than potassium. Thus, although 


the normal sea water has twenty times as much sodium as potassium, 
fish eggs often have quite twenty times as much potassium as 
sodium. There would not appear to be in this connection any dif- 
ference between homoio-osmotic and poikilo-osmotic aquatic animals. 
It is also obvious from Table 47 that aquatic eggs often have very 
much less salt in them than the ambient medium, and this would 
be a special case of the phenomenon found in all marine animals, 
and termed by Fredericq "Mineral hypotonicity". Bialascewicz 
arranged the animals he studied in a list of ascending concentration 
of metalHc ions as follows : 

Metal gramions 


per litre 

Octopus {Sepia officinalis) ... 


Gephyrean worm {Sipunculus nudus) 


Spider-crab {Maia verrucosa) 


Wrasse {Labrax lupus) 


Herring {Clupea harengus) (McCallum) 


Dogfish {Scyllium canicula) ... 


Sea-urchin {Arbacia pustulosa) 


Sea-urchin {Paracentrotus lividus) ... 


which would also be an ascending table of taxonomic groups, were 
it not for the high metal content of the echinoderm eggs, which 
exceed even the fishes. 

There are other points concerning the relative amounts of salts 
in the eggs which require mention. McCallum, who had for a long 
time previously been studying the proportion of salts in the ash of 
animals and parts of animals with reference to the composition of 
sea water both now and in earlier geological epochs, made an 
analysis of herring's eggs in 1926. He had previously differentiated 
between palaeo-chemical salt ratios in bloods, namely, ratios re- 
sembling that which pre-Cambrian sea water can be calculated to 
have possessed, and neo-chemical salt ratios, namely, ratios resembling 
the sea water of the present day. Thus Limulus polyphemus and Aurelia 
flavidula, the king-crab and the medusa, which have always been 
marine animals, now approach the modern sea in the composition of 
their vascular fluids, but the lobster Homarus americanus, the selachian 
Acanthias vulgaris, the frog, dog, and man, for instance, all have ratios 
resembling the composition of the sea water at the appearance of 
the protovertebrate form. He had also identified the kidney as the 
organ responsible for maintaining the palaeo-ratios in the salts of the 
blood. In order to explore the possibility of identifying a palaeo-ratio 


in the contents of the cell itself, he had recourse to eggs, and for those 
of the herring obtained the following distribution : 

Ratios on the basis of Na 100 

Na K Ca Mg CI 

100 216-7 ii'4 18-7 356-8 

This stood in marked contrast not only with the vertebrate blood- 
plasma but also with the Archaean sea water calculated for the 
time at which life first began to appear in it, thus : 

Vertebrate blood-plasma (dog) 

6-6 2.8 0-7 139-5 

Archaean sea water 

100 100-250 10 0-05 

But after extraction of the dried eggs with water in a Soxhlet 
apparatus, the determination of the ratio of salts in the soluble part 
gave results more like the ratio for the Archaean sea water: 

100 219-9 5'6 1-6 359-2 

McCallum therefore concluded that the soluble part of the ash of 
the herring's egg exhibits a palaeo-chemical ratio. The bond shown 
here between the metals and the organic substances is useful in 
reminding us that even in fish eggs, where the anion/cation ratio is 
well above unity, some of the metal as well as the acid radicles may 
be united in organic combination. 

The relation between the salts in the intermicellar fluid of yolk 
and those in the dispersed phase itself has been studied by Bialasce- 
wicz and by Vladimirov. Bialascewicz worked firstly with the yolks 
of Torpedo eggs, but also with those of the hen and the trout. He 
prepared series of mixtures of the yolk with diluents in different 
concentrations, such as isotonic solutions of lithium sulphate and 
lithium nitrate, or in some cases distilled water, and then, submitting 
the mixtures to ultra-filtration, he estimated the ash and its com- 
position in the filtrate and the residue. He first found that the 
percentage of chlorine bound to the dispersed phase in the ooplasm 
was practically independent of the degree of dilution, and from this 
fact he was able to calculate the volume of the intermicellar fluid 
of the yolk (see Table 48). For the hen's egg this was 0-549, per 

362 THE UNFERTILISED EGG AS A [pt. m wet substance, and for the egg of Torpedo ocellata a similar calcu- 
lation, based on cryoscopic experiments, gave a value of 0-482. On 
the basis of these figures, he proceeded to study the partition co- 
efficient of each individual ion as between dispersed phase and inter- 
micellar liquid. In Table 49 these partition coefficients are given; 
they represent the ratio amount of ion in the continuous phase or inter- 
micellar liquid j amount of ion in the dispersed phase. It will be noted 
from Fig. 17 that as dilution of the original yolk goes on the 
ratios in some cases change, but in others remain constant. Thus 
the chlorine of the trout and the hen egg yolk remains constant 
at 0-5 in the latter and 1-02 in the former case, showing that 

Table 49. Bialascewicz's figures. 










.2 ^ 


•2 ~ 



I -000 



I -000 



I -000 












I- 000 

I -000 











I- 000 


























I -000 



I -000 


I- 000 

I -000 


it is very stably combined in the dispersed phase, though in different 
proportions according to the animal. Thus there is considerably 
more chlorine in the dispersed than in the continuous phase of the 
yolk of the avian egg, while in the fish egg there is a very slight 
excess of chlorine in the continuous phase. In all other instances, 
however, both as regards the hen and the trout, the excess of ion is 
in favour of the dispersed phase, the colloidal aggregates of which 
may therefore be looked upon as reservoirs of ash. Nevertheless, 
there is a good deal of the sodium combined in the continuous phase, 
and not a little of the potassium, though here the trout differs from 
the hen, for the potassium ratio is about 0-9 in the former case and 
only 0-7 in the latter. All the other ions have lower ratios than 
these; magnesium, calcium and phosphorus, for instance, are all 
present to a much greater extent in the dispersed than in the con- 
tinuous phase. These experiments show also exactly how firmly the 
ions in the dispersed phase are bound there, and with what ease 
they may be washed out into the ultra-filtrate. It is apparent from 

SECT. l] 



S 2 °'^^ 

£ oT 0-8 - 


CO) 0-6- 

« E 



Bialascewic ^ 

Fig. 17 that the phosphorus, chlorine, and probably sodium in 
the dispersed phase, are intimately united there, for, however 
great the dilution of it, they do not increase in the ultra-filtrate. 
Magnesium and calcium, on the other hand, show a comparative 
readiness to pass out of the dispersed phase as the dilution is increased. 
The behaviour of the potassium is the most pecuHar, for, as dilution 
goes on, the calculated con- 
centration of this ion actually 
decreases, but as the decrease 
is slight it is probably due to 
experimental error, and it was 
treated as such by Bialasce- 
wicz himself. Thus, of the 
ions bound to the dispersed i | o-s 
phase, the cations sodium and 
potassium, and the anions of §? 0-3^, 
chlorine and (presumably) 
phosphate, are firmly attach- 
ed, while the cations calcium 
and magnesium are not, and 
can easily be washed out. 
The high proportion of phos- 
phorus in organic combination should be remembered here. 

Bialascewicz also pointed out that the partition coefficient or ratio 
followed with dilution a practically rectilinear course, so that some 
idea of the ratio in the natural undiluted yolk might be obtained by 
extrapolation. These figures so obtained are shown in Fig. 17, from 
which it may be deduced that the ions follow the order phosphorus, 
calcium, magnesium, chlorine, potassium, sodium, beginning with 
the one most of which is in the dispersed phase and ending with 
the one least of which is so distributed. 

Fig. 1 8 shows another aspect of the passage of ash from dispersed 
to continuous phase. 

In succeeding papers Bialascewicz extended these researches to the 
eggs of amphibia, some other fishes, Crustacea, molluscs, echinoderms 
and annelids. He reported that the intermicellar liquid varied much 
in its relative amount, accounting for from 20 to 63 per cent, of 
the whole ooplasm. From the data in Table 50, however, there 
does not seem to be a very close relation between the relative volume 

extrapolated 2 
values for undiluted 

4 6 

degree of dilution 

Fig. 17. 



[PT. Ill 







• — ■ «..;« 

of continuous phase and the percentage dry weight of the system. Bia 
lascewicz's tables give 
the concentration in 
percentages of the prin- 
cipal ions in the inter- 
miceliar liquid of dif- 
ferent eggs, and these 
are conveniently sum- 
marised in Fig. 19, 
taken from his paper. 
From this it is obvious 
that all the eggs studied 
have about the same 
proportion of potas- 
sium, but that the other 
ions are rather variable. 
There is much more 
calcium, relatively, in 
the continuous phase 
of the yolk of the hen's 
egg than in that of any 
of the others except the 
crustacean Maia verru- 
cosa. Similarly, there is 
more magnesium, relatively, in that of the frog than in any other egg. 
A very interesting comparison may be made between the distribution 
of ions in the continuous phase of the eggs and that in the serum of 

Table 50. Bialascewicz's figures. 

0-1 0-2 0-3 

Concentration of the bhree elements in 
the continuous phase (mgrnt per cc) 

Fig. 18. 


Continuous phase 

cc. per cc. 

In% of vol. 




% dry weight 

Scyllium canicula 




Salmo fontinalis 




Salmofario ... 


41-5 (Faur^-Fremiet & Garrault) 

Torpedo ocellata 




Acanthias vulgaris 



47-3 (Zdarek) 

Arbacia pustulosa 




Paracentrotus lividus .. 



22-6 (Wetzel) 

Rana temporaria 



42-6 (Kolb, Terroine, etc.) 

Callus domes ticus 



50-3 (Kojo) 

Sepia officinalis 



47-3 (Wetzel) 

Maia verrucosa 



43-6 (Wetzel) 

SECT, l] 



the corresponding adult animals. Fig. 20, taken from Bialascewicz, 
shows that the potassium preponderates in the former and the sodium 
in the latter, while the other inorganic substances are more or less 
equally distributed. As there is no difference in electrolyte con- 


-S 604 
















^= Potassium ^ = Calciu 

= Sod'rum 

Fig. 19 


= Magnesium 

centration between the continuous ooplasm phases of fresh-water 
and marine animals, one must conclude that salts do not 
account for the properties possessed by the latter, and that crystal- 
loidal organic compounds, such as taurine, urea and glycine, play 
an important part in keeping up a high osmotic pressure. Thus 
Bialascewicz found a concentration of 8-43 gm. per litre of urea in 



[PT. Ill 

undeveloped Torpedo ocellata eggs, but none in those of Arbacia, Sepia, 
or Maia. 

Vladimirov occupied himself with the egg-white in the egg of the 
bird. In connection with other investigations which dealt with the 

Salmo fonblnalis 


Torpedo ocellaba 

Maia verrucosa 

Continuous phase 
of egg-yolk 

Serum of adult animal 
Fig. 20. 

water metabolism of the egg (see Section 6-4) he measured the 
electrical conductivity of the egg-white in the unfertilised ovum, using 
the Kohlrausch and Holborn apparatus, and obtaining a value of 
7*6 X io~^. By the aid of a dialysis method he calculated the 
electrical conductivity of the intermicellar fluid of the egg-white, 
allowing for the disturbing effect of so large a concentration of pro- 


tein. The result came out to 10-4 x io~^. If this work were repeated 
for the yolk, interesting commentary on Bialascewicz's researches 
would be possible. It agrees with the earlier measurements of 
Bellini, who found the electrical resistance of the unincubated white 
to be Q. 1 8-8 ohms. Much further work on such properties of the 
yolks and egg-whites of a wide range of eggs is urgently needed, for 
they must obviously be of the greatest importance to the developing 
embryo. Such questions as the electrical conductivity of egg-cells 
and developing embryos are very relevant here, but must be left 
for consideration in Section 5. 

As a conclusion to this discussion of the chemical constitution of 
the egg, it may be admitted that great progress has been made in 
our knowledge with respect to it during the last fifty years. But to 
a discerning judgment, it remains none the less a matter for great 
surprise that in view of our comparative ignorance of the chemical 
architecture of the egg, we know as much as we do about the coming- 
into-being of the chemical architecture of the finished embryo. 

One further matter may be alluded to in this section. The com- 
position of fossil eggs cannot be said to have much embryological 
interest, but it is hard to exclude a mention of them. The only 
analyses we have are those of ZoUer who worked on the fossil eggs 
of Chincha Island, off the Peruvian coast, where seagulls have been 
living and depositing guano from a very remote date. Zoller found 
that "time, which antiquates antiquities, and hath an art to make a 
dust of all things" had had that effect on these eggs and had reduced 
their water content to 14-4 per cent. There was no urea or uric acid 
present, although the protein had nearly all disappeared and had 
given rise to ammonium salts. There was no trace of fat or of carbo- 
hydrate, and the sulphur of the proteins had all turned into sulphate. 





Phosphoric acid ... 


Total nitrogen 


Ammonia N 






These figures make it only too clear that if palaeontology and bio- 
chemistry enter into closer relations than exist at present, it will not 
be by way of the chemical analysis of fossil eggs. More hopeful 
approaches will be found in Section 9-15. 


2-1. Introduction 

We have so far been considering the unfertilised egg-cell and its 
reserves of nutrient material as a physico-chemical system, and we 
must now proceed to summarise critically what is known about 
the alteration the egg undergoes in passing into the state of the 
finished embryo. Subsequent sections will take up the chemical 
changes during this process in all their complexity, but first the 
apparently simple phenomena of change of weight must receive con- 
sideration. To this undertaking special difficulties are attached; for 
example, the act of birth or hatching itself, important though it is 
for the chemical embryologist as the term of his investigations, is yet 
purely arbitrarily and conventionally chosen as such, and, as far as 
the organism itself is concerned, may be relatively unimportant. The 
age at which birth takes place varies in different animals consider- 
ably, and may occur earlier or later in development, cutting across 
cycles of growth at almost any point. However, the study of growth 
in weight and alteration in shape, is an essential preliminary to the 
study of the chemistry of the embryo. I do not propose to spend 
any time in the discussion of definitions of growth. 

The actual data which we have concerning pre-natal growth 
will be found in Appendix i, where they have been placed in 
the hope that a collection of them will be of assistance to chemical 
embryologists. No previous assemblage of them has been made, and 
they are to be found scattered all through the literature. Biochemists 
have in the past been insufficiently careful to check their results on 
embryos against normal tables of weight, length, age, etc. 

The predecessors of this section are the chapters on growth in 
d'Arcy Thompson's Growth and Form and Faure-Fremiet's La Cinetique 
du Developpement. These authors gave a full criticism of the whole 
subject, but without special reference to the development of the 
embryo. Moreover, much has been done since they wrote, and their 
treatment differs in various ways from what follows here. 


It is obvious that the growth of an embryonic organism can be 
measured in many ways besides that of increasing weight. Its en- 
larging dimensions in various directions of space can be measured, 
or its volume, or the quantity of various constituent substances. More 
will later have to be said about the way in which these different 
quantities may be thought of as fitting in together and changing 
with age. But the simplest manner of representing growth will 
probably always remain the measurement of the increase in weight 
of the total mass, and it is this which is now to be considered. The 
relation of this factor to the age and the length of the foetus is a 
point of capital importance to the chemical embryologist in the 
knowledge of his material. It is true that the data are fragmentary 
enough, restricted as they are almost entirely to various mammals 
and the chick. 

2'2. The Existing Data 


Octopus. A remarkably complete set of data for the embryonic 
growth oi Sepia is given by Ranzi, and this is almost all we have as 
regards invertebrate development. 


Silkworm. Luciani & LoMonaco have studied the curve of growth 
through the successive moults in the larval condition, but, in spite 
of their work and of many other researches on the silkworm larva 
and ^gg, I cannot find any in which the increasing weight of the 
embryo itself has been measured prior to hatching. 


Trout. Weighings of fish embryos have been exceedingly few in 
number, owing to the smallness of their size and the difficulty of 
separating them from the yolk. Kronfeld & Scheminzki, however, 
have made some estimations of the increase in weight of trout 
embryos, and their figures, together with those of Gray, are shown 
in Table i of Appendix i. 




[PT, m 


Frog. In the case of amphibia, where the cleavage in the egg is 
more or less inclusive of the yolk-laden portion, it is not possible to 
obtain data for the weight of the embryo itself, for, before hatching, 
although the protoplasm is constantly increasing at the expense 
of the yolk, the two elements cannot be separated, and therefore 
cannot be weighed in isolation. This appears in the figures of Faure- 
Fremiet & Dragoiu ; Schaper ; Davenport ; and Bialascewicz, and 
must always be taken into account when differences between species 
in water-content and other constants are under consideration, for 
much confusion may be caused by not distinguishing carefully 
between yolk plus embryo and embryo alone. 


Snake. Bohr's very few figures on Coluber natrix are all that are avail- 
able. (Appendix i. Table 2.) 


Chick. It is on this animal, as might be expected, that the greater 
part of the work on embryo- 
nic growth has been done. 
Hasselbalch, in the course of 
his work on the respiration 
of the chick embryo, ob- 
tained a regular series for a 
race not given. These corre- 
sponded well enough with 
the earlier data of Falck (also 
from an unknown breed), 
which were the first to be 
published, appearing in 1857. 
Hasselbalch's curve is shown 
in Fig. 21, in which for the 
first time we see the usual 
' ' embryo-placenta relation ' ' 
in the form of a weight of 
extra-embryonic structures 
larger than the embryo in the 
earliest stages, but soon falling below it.^ 
relation between the two as follows: 





O Membranes 
• Embryo 

Hasselbalch calculated the 

See also Fig. 521. 


Wt. of embryo + wt. of membranes 


Wt. of embryo 




I -108 





Other sets of weight data have been reported by Lamson & Edmond, 
by Murray and by Needham, for White Leghorn chicks, and by 
LeBreton & Schaeffer for chicks of an unspecified race. These are 
all placed in Table 3 of Appendix i, where it will be seen that the 
general agreement between them is good. The values obtained by 
Murray; Byerly^ and Schmalhausen are probably the most accurate, 
for the conditions were very carefully controlled. Hanan's values are 
lower than all the others. It is unfortunate that Schmalhausen does 
not state what breed of hen was used in his experiments, though he 
does mention that it was not genetically pure. Some early measure- 
ments by Welcker & Brandt are not included in the table, for they 
do not appear to be trustworthy. 

Other measurements which are useful are those of Edwards, who 
has published a peaked curve showing the length of the primitive 
streak during the first 50 hours of incubation. ^ Schmalhausen's work 
on the growth of parts of the chick embryo will be dealt with later : 
he was preceded by Falck, who measured and weighed various 
organs but did not use enough material to make his figures valuable 
to modern workers. 


[a) Mouse. In 1923 LeBreton & Schaeffer published figures for the 
embryonic growth of the mouse, but these were not very numerous. 
The only other work on this subject is that of McDowell, Allen & 
McDowell, probably the most accurate and satisfactory study of pre- 
natal growth in any form that at present exists. Their figures are given 
in Table 4 of Appendix i, and the curve obtained from them in 
Fig. 22. This is drawn on arithlog paper, the ordinates in logarithmic 
ruling giving the actual weights in gm., the abscissae in arithmetical 
ruling giving the age and the number of the individuals. On each day 
the range of the individual unclassified weights is shown by a vertical 
line which is itself used as a base-line for the frequency distribution 
of the classified individual weights. The number of cases in the 

^ See also Fischel and Leva. 




[PT. Ill 

distribution is shown by the distance to the right of the vertical base- 
Hnes, and can be judged by the frequency-scale at the bottom of the 


1 -000 










\-y^ ^^^ 






, zz 


- k/^ 


V^Z ' - 











.c;r.Al E np FRFniifNniF'=^ 

1 I 1 1 1 1 1 1 1 1 1 1 1 1 

20 40 60 


9 10 n 12 13 14 15 

Fig. 22. 

16 17 18 19 

chart. The means, weighted by the number of individuals in each 
litter, are shown as dots on the vertical base-lines, and it is through 
these, of course, that the "normal curve" would be drawn. The 
continuous curve in the graph is one drawn to a formula which 

SECT. 2] 



Foetus of albino rab 

will be discussed later, in Section 2-4 (p. 393). The lay-out so 
made reveals several interesting features; it appears, for example, 
that there are always individuals on a given day which are equal 
in weight to the mode of the day before. McDowell, Allen & 
McDowell consider that this is evidence of a possible delay of as 
much as 24 hours between copulation and fertilisation, but, whether 
this is so or not, it certainly equates with exactly similar variations 
found in the chick both in the early stages (primitive streak) and in 
the later ones of organ-growth. Further, the modes and means are 
generally close together, though less so at the beginning of develop- 
ment than at the end, and the latter do not approximate to a straight 
line. A glance at the graph also shows that the highest individual 
weights on each day tend to form a curve parallel with that of the 
means throughout development. 

(b) Rat. Donaldson's comprehensive monograph of 191 5 includes 
a discussion of the growth of the rat embryo, but much less work 
has been done on this animal 
than upon man, for in the latter 5 
case the ad hoc labours of ob- 
stetricians have often provided 
much valuable material for the 
biologist. However, Stotsen- 
berg's work gave a good account 
of the matter, and his figures 
are reproduced in Table 5 of 
Appendix i, and in Fig. 23. 
They begin from the 13th day 
after insemination, before which 
weighing is difficult, and they 
continue until birth, which takes 
place at the 22nd day. This pre- 
natal period would appear to 
be one complete growth-cycle, if we may judge from the work of 
Donaldson, Dunn & Watson on the post-natal growth of the rat. 

Huber has studied the growth of the rat embryo in its earliest 
stages prior to fixation to the uterine wall. He states that the egg- 
cell of the rat approaches the uterine end of the oviduct while in 
the two-cell stage, segmentation being slow and proceeding as the 
transit takes place. Fig. 24, reproduced from his monograph, is a 

16 17 18 
Fig. 23. 



[PT. Ill 

photograph of a model of the oviduct with its contained eggs. By 
reconstruction methods at a magnification of looo diameters of the 
ova Huber was able to determine the volume changes during seg- 
mentation as follows: 



^ , 



Average vol. 
(cubic mm.) 
















1 1 -cell 


There would, therefore, appear to be a certain increase in volume 
during these very early stages, but as the specific gravity changes 
are not known it is difficult to understand what it may imply. There 
is at present a great gap in our knowledge of the embryonic growth 

Fig. 24. 

of the rat between the early point at which Ruber's studies end and 
the later one at which those of Stotsenberg begin. Huber himself 
suggested that the slow development of the ovum of the rat during 
its passage down the oviduct was best accounted for by the lack of 
any food-supply for an alecithic egg until fixation to the uterine wall 
had taken place. As the whole embryonic period of the rat is only 
22 days, it is of great interest that the first four days should involve 
hardly any increase in size. This fact renders of no significance the 
calculated weights of rat foetuses given by Donaldson, Dunn & 

SECT. 2] 



Watson in their earlier paper, for, in assuming that embryonic growth 
in the rat followed a quite similar course to that taking place in 
man and the rabbit, they did not allow for the long time taken for 
the rat egg to pass through the oviduct after fertilisation. Thus they 
arrived at the result that the rat embryo of 15 days should probably 
weigh 2-6 10 gm., whereas by direct measurement Stotsenberg found 
that it only weighs o- 1 68 gm. Their calculated figures are consequently 
not included in Appendix i. 

(c) Guinea-pig. The most usually quoted work on the embryonic 
growth of this animal used to 
be that of Read, who used 
a very indirect method of 
measuring it. He weighed the 
pregnant female every day be- 
tween insemination and birth 
and then each foetus with its 
membranes and fluids, from 
which data, assuming that 
growth had taken place regu- 
larly, the weight of one embryo 
could be calculated. He con- 
cluded that the guinea-pig 
passes through two growth- 
cycles during its intra-uterine 
life. But no satisfactory conclu- 
sion can really be drawn from 
such figures, subject as they are 
to all kinds of complicating 
factors, and, like the earlier 
ones of Minot on the guinea- 
pig, obtained in the same in- 
direct way, they are better 
discarded. It is needless to point out that differences in the weight 
of mother + embryo due to defaecation, filling of caecum, etc., may 
amount to grams, while the weight of the embryo is still only 
milligrams. In the absence of any other figures, they had their 
importance, but in 1920 Draper made a complete study of the 
embryonic growth of the guinea-pig. Together with the few frag- 
mentary (but direct) figures of Hensen, and the careful work of 






• / 

• / 
/ • 



/ • 


- E 




- C 




A * 




• / 

• / 





















Fig. 25. 



[PT. Ill 

Ibsen, and Ibsen & Ibsen, Draper's figures form the standard series, 
and are shown in Tables 6 and 7 of Appendix i. As is generally 
known, the guinea-pig differs from most other mammals in being 
born much later in its life-span than is usual, so that its lactation 
period is exceedingly short and it is able to eat green food a very 
few days after its birth. This is reflected in its gestation time which 
is relatively long. 

20 '0 

CO / 








® / 


'^ / 






— c 



K®/ - 

^ • uv- of 'membranes 





IX, Age ab which wbs. of embryos &, 


membranes are equal 




Aqe in days 





35 40 
Fig. 26. 




60 65 

During the 64 days of its development in utero, the guinea-pig 
increases its weight to about 85 gm. and its length to 10 cm. This 
process is shown in Fig. 25 taken from the figures of Draper. In 
Fig. 26, which gives an enlarged view of the lower part of the growth- 
curve, the increase in weight of the placenta, the membranes, and 
adnexa, together with the amniotic and allantoic fluid, is also shown. 
The extra-embryonic structures reach a more or less constant weight 
about two-thirds of the way through development, but, as can be 
seen from Table 5 of Appendix i, the values from which this curve 
was drawn are very divergent. In comparing the growth of the 

SECT. 2] 



embryo with the growth of the membranes, it is interesting to see 
that for the first month the latter weigh much more than the former, 
after which, for a certain period, they grow together at the same 
rate. But soon the curves diverge, and the membranes hardly grow 
any more, while the embryo continues to increase greatly in size. 
Evidently when the membranes and placenta have reached a sufficient 
size to meet the utmost further demands of the embryo they grow 
no more. There can be little doubt that the size of the placenta 
exercises an influence on the growth of the embryo, and is of the 
highest importance from the point of view of embryonic nutrition. 

The amniotic liquid bears the same relationship as regards weight 
to the embryo as do the placenta and the membranes. 


Fig. 27. 

Fig. 27 shows Draper's curve for the length of the embryonic 

Ibsen's work led to much the same conclusions as regards the 
relations between embryo and adnexa as that of Draper. Ibsen 
found that the number of foetuses in the uterus exerted an effect 
on the growth-rate of each one, thus the larger the litter the slower 
the rate of growth of the individual foetus. The early growth of the 
placenta is more rapid than that of the foetus, but they reach the 
same weight on the 25th day, after which the foetus outstrips the 
placenta very soon. Placental weight and the weight of the mem- 
branes towards the end of pregnancy are closely correlated with 
uterine crowding, but this is not the case with the decidua basalis, 
which corresponds to the maternal part of the placenta. Minot con- 
sidered that the amniotic fluid of the cow and of man decreased in 



[PT. Ill 

amount after the middle of pregnancy, but this was not found to 
be the case by Ibsen for the guinea-pig. Ibsen constructed from his 
experimental data the interesting diagram shown in Fig. 28, which 
shows the percentage of the whole system occupied by embryo, 
placenta, decidua basalis, and amniotic fluid from the 20th day 
onwards. The embryo does not rise in per cent, after the 55th day, 
the placenta remains very much the same all through, the decidua 
basalis is much smaller relatively at the end than at the beginning 

and so is the amniotic fluid. Up to the 50th day Ibsen found no 
correlation between foetus-weight and placenta-weight, but after- 
wards there is undoubtedly such a correlation, evidently due to 

[d) Rabbit. Much less work has been done on this form than might 
have been expected from its easy availability, but the figures of 
Chaine (the standard ones) are given in Table 8 of Appendix i, 
together with some early fragmentary ones of Fehling. Friedenthal 
also gives a few data which are shown in Table 9. 

{e) Dog. Liesenfeld, Dahmen & Junkersdorf made a thorough 
study of (unfortunately only 5!) dog foetuses. 

SECT. 2] 



(/) Sheep. As early as 1847 Gurlt made a study of the increase in 
length of the foetus of the sheep, but Colin is the only investigator 
who has ever determined the 
growth in weight (see Fig. 29). 
Gurlt's figures, which are quite 
regular, are given in Tables 10 
and II of Appendix i. Faure- 
Fremiet & Dragoiu, in the 
course of their extended work 
on the growth and chemical 
development of the embryo- 
nic lung in the sheep, made 
measurements of the growth 
of that organ, but did not give 
any data on the weights of their foetuses as a whole, a very unfortunate 
omission in view of the incompleteness of the literature on this 

[g) Pig. The only extensive figures in existence for the embryonic 
growth of the pig are due to the careful work of Lowrey and of 
Warwick. These are given in Tables 12 and 14 of Appendix i. 
Lowrey's results will again be referred to in connection with the 
growth of individual organs and parts in the embryo. LeBreton & 
Schaeffer also measured and weighed a certain number of foetuses in 
the course of their classical work on the behaviour of the chemical 
nucleo-plasmatic ratio during 

60 100 

Days, Sheep (Colin) 
Fig. 29. 

embryonic development. Their 
figures are shown in Table 1 3 of i 
Appendix i. \ 

(Ji) Cow. The embryonic \ 
growth of the cow has been \ 
investigated by several workers - 
whose results are shown in ' 
Table 15 of Appendix i. 

Fig. 30, constructed from 
Franck and Hammond, should 
be compared with Fig. 28 for the guinea-pig. 

{i) Man. The embryonic growth of man has been much studied, 
and many thousands of embryos have been weighed. His's studies 
have been the principal means of fixing the relation age/length, 

Months, Cow (Hammond). 
Fig. 30. 



[PT. Ill 

and Balthazard also gives figures for this, which will be found in 
Appendix i (Table i6). The earlier workers, Ahlfeld; Fehling; 
Hennig; Legou; Faucon; and Michaelis all obtained valuable data, 
but it was not until 1909 that a critical examination of them was 
made by Jackson who analysed the figures of his predecessors, and 
added a large number of new ones. His results gave a continuous 
curve from the earliest stages till birth, which agreed with the 
majority of the other investigators, but not perhaps with Hennig's 
curve (he gave no figures), 
which showed a very distinct 
slackening of growth about 
the sixth month, after which 
the same rate was resumed. 
If this phenomenon is real, it 
may possibly be associated, 
as Donaldson has suggested, 
with a transition from one 
growth-cycle to another, at 
the end of the sixth month, 
when the absolute weight 
begins to rise so rapidly. On 
the other hand, the mass of 
data which Quetelet and 
others after him have ana- 
lysed regarding the growth 
of man throughout life, would seem to show that there are three 
growth-cycles only, one pre-natal one, one with its maximum at 
5*5 years, and the third with its maximum at 16 years. Vignes' 
S-shaped curve for human embryonic growth is shown in Fig. 31. 

Bujard in 19 14 made a geometrical analysis of the early stages of 
the human embryo. 

Jackson measured the volume and weight of all the specimens in 
his own collection, and for the early stages also the volumes of the 
His-Ziegler models. His figures are given in Tables 17 and 18 of 
Appendix i, and the curve which he constructed from his own data 
as well as those of previous investigators is reproduced in Fig. 32. 
The 1 6th table of the appendix shows the volumes of the His- 
Ziegler models, and demonstrates that the human embryo, like all 
others, is much exceeded in size by the yolk-sac during the earliest 












- C 











1 _. 1 

260 280 300 
1 1 i > f 1 1 1 ■ 

3 4 5 

Fig. 31- 

.270 290 310 


SECT. 2] 



stages of development. Jackson, who adopted the Minot method 
of measuring the growth-rate, concluded that the rate was 9999 per 






























: \ 




/ !j 



AhlfelcL's dauta. 
■ehling's da-bet 
Jaxjkson's data, 
L.egoas data, 
Michael is' data 


1 * 







1 1 

1 1 

! 1 



1 / 
/ / 
/ / 





i / 

1 / 

/ / 
/ / 

''7 / 


' / 










' • 

50 75 1( 

125 150 175 200 225 250 275 
Age in Days 

Fig. 32. 

cent, for the first month, 74 for the second month, and 11 for the 
third month. This was in general agreement with the point of view 
taken by Miihlmann, and Jackson emphasised it further by showing 
that, if the weight of the embryonic membranes and fluids was taken 



[PT. Ill 

into account, the growth-rate for the first month was 574,999 per 
cent. What meaning can be attached to the enormous growth-rate 
figures which always appear when the Minot method is used for very 
young embryos must later be discussed. 

Fig. 32, which collects together the data of many observers, shows 
a considerable measure of unanimity between them. Ahlfeld's 
figures are the only ones which show serious divergence, and they 
were not taken into account by Jackson in his preparation of the 
"normal curve". Fig. 32 shows also by points the volume of the 
embryo at the different stages, but it does not differ much in value 
from the weight in grams. The specific gravity of the foetus does not, 
according to Jackson, remain precisely the same throughout develop- 


merit, but changes from very slightly above i-o in the early stages 
to 1-05 in the later ones. Probably this is associated with the pro- 
gressive loss of water as the embryo develops. 

One of the first to investigate quantitatively the growth of the 
human embryo was Boyd in 1861, who studied the weights of all 
the principal organs in embryos from 8*5 to 85 oz. He did not give 
figures for individual embryos from which a curve could be con- 
structed, but simply divided them into large groups such as "pre- 
maturely-born", etc. Legou's data, already referred to, were worked 
over again in 1903 by Loisel. Zangemeister, more recently, has 
published figures for human embryonic growth — these are shown in 
Table 17 of Appendix i. 

Other data for embryonic growth in man will be found in the papers 
of Fesser ; Toldt ; Meyer ; Heuser ; Bedu ; Sombret ; Arnoljevic ; 
Stratz; Borri; Corrado; Balthazard & Dervieux; Ecker; Hamy; 
Kolliker; Cruickshank & Miller; Browne; and Friedenthal. Scam- 
mon & Calkins, who have made a great many measurements in 
recent years, have constructed a three-dimensional isometric pro- 
jection, from which the height, weight and age of a human embryo 
may be read off if any one of them is known (see Fig. 33). The best 
recent paper on the whole subject is that of Streeter. 

Sandiford has shown that the weights and surface areas of foetuses 
fall on straight lines when plotted on double log paper. For further 
information on surface growth see Scammon & Klein. 

(j) Whale. Some information on the embryonic growth of the 
whale is contained in the papers of Harmer; Risting; Hinton; and 
Mcintosh & Wheeler, but it mostly concerns increase in length. 

2-3. The General Nature of Embryonic Growth 

We may now turn to the theoretical aspect of the matter in the 
attempt to find out what interpretation can be placed upon them. 
We may in the first place take as a simple example of an embryonic 
growth-curve the work on the growth of the chick (White Leghorn) 
of H. A. Murray. Table 51 shows, firstly, the actual weights of the 
embryos on each successive day, secondly, the amount gained in each 
such 24-hour period, i.e. the amount of substance actually added on 
to itself by the embryo during the lapse of the time in question. This 
is known as the daily increment. In the next column the averages 
of the daily increments are placed, and these figures, known as the 

384 ON INCREASE IN SIZE [pt. hi 

mid-increments, represent for each point which begins one period 
and ends another how much substance the embryo is adding on to 
itself between the times (a) half-way through the last period, and 
(b) half-way through the period to come. In other words, the mid- 
increments convert the daily increments into terms of the points 
instead of the spaces between the points. If now the mid-increments 

Table 5 1 . Growth of the chick embryo ( White Leghorn) . 
H. A. Murray's figures. 






Wet weight 

Dry weight 



of dry 

in days 



(dry weight) 

(dry weight) 





























































1 1 ,460 


























are expressed as percentages of their actual weights of embryo at 
their corresponding points in time, the last column or percentage 
growth-rate is obtained. This last calculation is, as will be seen, the 
only one so far made in the table which is open to serious criticism, 
and it is associated with the name of C. S. Minot, who was the first 
to propose it as a satisfactory measure of the growth-rate of an 
organism. When these figures are plotted the curves shown in Fig. 34 
appear. The actual growth of the embryo expressed in terms of its 

SECT. 2] 



weight at any given moment gives a curve which rises steadily till 
the observations cease without betraying much sign of any slackening. 
But the increment curves, on the other hand, show an unmistakable 
S-shape which is due to the fact that, for the earlier periods, the 

— o AbsoLate weight gms. wet 
• >> )> j> dry 

— Dajly incremenbl 

^ « Mid » r^^- 

Fig. 34- 

weight gained each day is very little more on one day than the gain 
on the previous day, while, towards the middle of development, the 
daily increments and the mid-increments vary much more, each one 
being considerably higher than the one before. On the other hand, 
when the end of development is approaching, the increments each day, 
though far higher in absolute amount than those which were made 
in the early stages, do not differ so materially from one another, with 

NEI 25 



[PT. Ill 

the result that the curve slackens off and enters a slowly-rising phase 
again. It is possible, of course, to calculate the average daily incre- 
ment for the whole developmental period (see Table 52), and the 
figures so obtained have been made the basis of a comparison of 
animals by Friedenthal. The fourth curve, that of the percentage 
growth-rate, Minot's curve, as it may be called, begins at a high 
level and continually descends, although in this instance there is a 
slight kink on it midway through development, which may for the 
moment be disregarded. All Minot curves begin at a high level and 
descend as development proceeds. Now, in many cases, it may 
happen that not only the increments but also the whole growth- 
process itself slackens off towards the end of the period taken, in 
which circumstance the curve relating weight of animal at any 
given time to age will also have an S-shaped form. It has not 
escaped the perspicuity of those who have considered these pheno- 
mena that this S-shaped curve has a resemblance to the S-shaped curve 
of an autocatalysed monomolecular reaction, and this likeness will 
shortly be taken up at length. 

Table 52. Average daily increments. 
Friedenthal's figures. 











Ermine ... 


Sheep ... 


German marmot 














Stag ... 




Horse ... 




Hippopotamus . . 




Camel ... 






A more complicated example of the various types of growth-curves 
is afforded by Fig. 35 taken from Brody. It shows the growth 
throughout the life-span of the albino rat. The curve passing through 
the circles shows the course of growth ; it is, in fact, the weight of 
the whole animal at any given moment plotted against the age 
at that moment. The strongly indented curve, passing through the 
crosses, is the line showing increment in unit time. In the data of 
Murray for the embryo chick the absolute growth-curve rises steadily. 

SECT. 2] 



and has no slackening off or self-inhibitory phase; the increment 
curve is therefore singly sigmoid. But here, when the absolute 
growth-curve is itself sigmoid, the increment curve is symmetrically 
sigmoid, rising to a maximum and then falhng away again to zero 
during the second phase. Finally, the corresponding Minot curve is 
shown by the line joining the triangles, and, as usual, it declines 
throughout growth from an initially very high value. 

n 70 










2 40 






DaysO 10 20 30 40 50 60 70 80 90 100 HO 120 130 140 150 160 lyO^lB0 190 200 210 220 
o 8 18 28 38 48 58 68 78 88 98 108 118 128138148 158 168 178 188198 

% I Age 


Fig- 35- 

There are other ways, however, in which the subject of embryonic 
growth-curves can be introduced. Ostwald's classical work on 
growth in metazoa, which appeared in W. Roux's "Vortrage" 
series in 1908, laid great emphasis on the value of knowing the 
precise route through weight taken by an organism on its way 
from egg-cell to finished embryo. In Fig. 36, taken from his mono- 
graph, several different curves are shown relating time to weight. 
At the time A, at hatching or birth, for instance, the weight of the 




[PT. Ill 

organism is exactly the same in all four cases, but the manner in 
which the increase in weight has taken place is in the four cases 
profoundly different. It is certainly quite clear that the chemical 
embryologist, engaged in the attempt to understand the processes 
which contribute to the final result, must pay detailed attention to 
the path by which this final 
result is arrived at. The four 
different curves in Ostwald's 
figure would imply four very 
different sets of conditions with- 
in the developing embryo. An 
embryo which grew according 
to Curve I would change very 
rapidly in the beginning, and 
afterwards change progressively 
less rapidly as the curve became 
asymptotic. The reverse of this 
process would happen if the em- 
bryo grew according to Curve ii, 
for there the process continually increases in rapidity, and is pro- 
ceeding at its fastest when the point A is reached. Curve iii, on the 
other hand, being S-shaped, would seem to indicate the presence of 
an autocatalytic process, for at first the growth proceeds faster and 
faster, but later on, after the point of symmetry of the curve has 
been reached and passed, slower and slower. Several such S-shaped 
curves superimposed on one another make up Curve iv. 

As far as is known, no growth takes place in the manner repre- 
sented by Curve i, but rather in that of the other three curves, 
though our present knowledge does not enable us to say definitely 
which, except in certain cases. Ostwald's monograph should be 
referred to by those who wish to see how he continued the discussion 
of growth-curves, for it is probably the best presentation of the subject, 
and it was certainly written from a much less doctrinaire point of view 
than most of its successors. 

The general interpretations of embryonic growth-curves may be 
divided into several classes. They depend more than anything else, 
as will be clearly seen, upon how the facts are expressed. One way 
of expressing them led Minot to his "laws of cytomorphosis", 
another led Robertson to his "autocatalytic master-reaction", 


and, more recently, still other ways have been devised. The un- 
prejudiced investigator cannot avoid a considerable measure of 
scepticism in considering the claims of one way of expressing the 
facts over another. 

2-4. The Empirical Formulae 

We may first direct our attention to those presentations of the facts 
which do not carry with them any theoretical superstructure, but 
aim simply at describing the data in as short a manner as possible. 
The first of these "empirical formulae" was that of Roberts, who in 
1906 pointed out that the growth of the human foetus could be 
regarded as nearly proportional to the cube of the age ; thus, if the 
weight in grams is W and the age in days T, the formula would be 
W — T^. But this was only very approximate, and the curve it gave 
did not fit the curve drawn through the experimental data with 
any accuracy. Roberts, indeed, stated that his formula gave results 
correct to "within an ounce at the third month". "Since the weight 
of an embryo of the third month," was Meyer's remark, "according 
to the best available evidence, is considerably less than an ounce, the 
accuracy of Roberts' method must be fully apparent without further 

Tuttle next introduced an equation in which arbitrary constants 
were introduced, thus W = 50 {T — 2)^. Later still, Jackson, whose 
work on the human embryo has already been mentioned, proposed 
the formula : 

where W is the weight in grams and T the age in days. This fitted 
the experimental points much better than the formulae of Roberts 
and Tuttle, but was still rather deficient, especially in the very 
early period and the very late period. Henry & Bastien also pro- 

x^ + 2^xj> — 3q>'2 — i62y = o, 

where x = months andj = kilos. 

Duvoir has reviewed the other more or less practical rules which 
have from time to time been proposed, such as Casper's rule that, from 
the fifth month onwards, the age of an embryo in man can be found 
by dividing the height in centimetres by 5. Balthazard & Dervieux 

390 ON INCREASE IN SIZE [pt. iii 

altered this formula to 5-6. Again, Mall's rule states that the number 
of days embryo age is equal to the square root of the foetal total 
length in centimetres x 100. Balthazard & Dervieux have also 
evolved formulae relating foetal age to the length of the limb-bones, 

L = femur length x 5-6 + 8 cm. 

L = humerus length x 6-5 + 8 cm. 

L = tibia length x 6-5 + 8 cm. 

The use of empirical formulae in the description of human foetal 
growth has been carried to its greatest refinement in the work of 
Scammon & Calkins, whose formula, 

n- 2-5/, L2 

holds with great exactitude from the third month onwards. Another 
of their formulae, 

T = 2-134 X o-iZ X o-ooiiL^, 

holds with rather less exactitude from 2-5 foetal months onwards. 
In both these cases, T is the menstrual age in lunar months, L the 
total or crown-heel length of the dead body in centimetres. They also 
found that 

W= (o-26L)3-i'>8 + 4-6, 

3 108 , 

or Z, = 3-846 VW - 4-6, 

where W is the weight of the dead body. From these equations, it 
follows that 

3 108/ 15S4 / 

T= 2-134 + 0-3846 VW — 4-6 + 0-01627 VW — 4-6, 
or T= 3-0 + ^•04.gVw — 0-012, 
orW= 0-561 — 0-366 T X 0-061 T^. 

The formula of Donaldson, Dunn «& Watson, for the post-natal 
growth of the white rat- up to 80 days, W = a + bT + cT^, and after 
80 days, W = a log T — bT — c, was of the same type as the other 
equations mentioned, but it had the additional refinement of in- 
cluding constants, a, b and c, which were variable according to sex 
and other factors. 

Murray, in his study of the chemistry of embryonic development, 

SECT. 2] 



found that his series of chick embryo-weights could be accurately 
described by the equation: 



or W=KT^-\ 
where K = o-668. 

This was not unlike the Balthazard-Dervieux formula for the 
human embryo: 

T= 19-4 X \^W. 

Diojs 5 

10 U t2 13 14 

Incub&lion 2052 
Fig- 37- 

Murray plotted the log. wet weight against the incubation age, and 
obtained a curve concave to the abscissa (see Fig. 37) corresponding 
to the curve which McDowell, Allen & McDowell got for the mouse 
embryo (see Fig. 22). He also found that the relation of log. weight 
to log. age was a straight line as far as his series of weighings went, 
and showed that the weighings of Hasselbalch and of Lamson & 
Edmond fell on the same straight line (Fig. 38). Murray's formula 
gave very good agreement with his figures, but these did not extend 
further back than the fifth day of incubation. When, later, Needham 



[pT. m 

and Schmalhausen made weighings of embryos between the second 
and the sixth day of incubation, it was found that Murray's formula 
did not hold for these earlier stages. Fig. 39 taken from the paper 
of McDowell, Allen & McDowell, illustrates this point. The broken 
line is drawn to Murray's formula, and the dotted line is an extra- 
polation of his curve which I made on the assumption that embryos 
grew at the same rate before 5 days as between 5 and 7 days, i.e. 
exponentially. The circles with dotted centres are the values experi- 
mentally obtained by me, the dots are those obtained by Schmal- 
hausen, and the cross within a circle is Murray's earliest figure. 




3 J.4 






















X LSkiDSon i Ldmond (a^vep^oe of lo embrvos) 
• H&ss2lbailch (sln^l? ojeigninos) 
Single cuci§hin§s l^ken in the course 
of other experiments in this series ■ 









0.65 0.70 0.75 

0.85 0.90 . 0.95 1.00 1J)5 

L05 incubation a^e (dsajs) 
Fig. 38. 



1.25 UO 

Murray's formula gives a line consistently above the experimental 
points for this early period, and the exponential extrapolation is quite 
at variance with them. But McDowell, Allen & McDowell evolved 
an equation which fitted these early points (the solid line) as well 
as all the later ones, as follows : 

log W = 3-436 log {10 (r- 0-5)} + 7-626. 

This new equation was based on an entirely different viewpoint 
from that of previous workers. McDowell and his collaborators 
regarded not "conception age" but "embryo age" as the right zero 
hour to take in growth calculations. It had always been assumed 
previously that conception or even insemination was the right 
starting-point, and Brody & Ragsdale and Brody based their method 
for finding age-equivalence in animals on this view, while Friedenthal 

SECT. 2] 



had shown a similarity in relative growth-rates by plotting the log. 
weights against log. conception ages. McDowell and his colla- 
borators, on the other hand, suggested that the time of growth ought 
rather to be calculated from the time at which the embryo first 
begins to have an axis, i.e. from the primitive-streak stage. Thus the 
major differences between the pre-natal growth of the guinea-pig, 


• 80 

■ 60 

■ 40 
- 20 




©85 077 ©88 © ©83 

77 ffi200 

Fig. 39- 

the mouse, and the chick would be accounted for by the varying 
times taken to get through the preliminary work of arrangement and 
organisation. Processes such as gastrulation, according to this view, 
would involve a law of growth so different from the later axial type 
that no formula should be expected to cover the two. We have already 
seen in the case of the rat's egg that some considerable time may 
elapse between the time of fertilisation and that of fixation to the 
uterine wall, during which the supply of nutrient material may be 

394 ON INCREASE IN SIZE [pt. iii 

very different from what afterwards obtains during embryonic develop- 
ment. There is, therefore, much justification for the view of McDowell 
and his collaborators. Brody himself had come nearly to this position 
without recognising it, for, in a paper published in 1923, he had 
pointed out that, during a short period in the early stages of growth 
(or regeneration) the apparent observed speed seems to be slower than 
would be expected. Thus the curve of the fitted equation cuts the 
time axis not at zero, the beginning of growth, but a little later. He 
advanced the explanation that Durbin had already applied to the 
initial slow phase in the regeneration of tadpole tails, namely, that a 
"cap of embryonic cells" was first formed, following in its growth 
quite different laws from the subsequent process as a whole. "It is 
suggested", said Brody, "that the apparent initial slow phase of 
growth of the individual from the fertilised egg is due to a similar 
qualitative growth." 

(Estimated weights of eggs are shown in Table 53.) 
McDowell and his collaborators proceeded to show that a similar 
formula would fit very well the curves of growth for the guinea-pig 
(Draper; Hensen; Ibsen & Ibsen), the mouse (McDowell, Allen & 
McDowell) and the chick (Murray; Needham; and Schmalhausen). 
For the mouse it was : 

log W = 3-649 log {10 (^ - 7-2)} + 8-6587; 

and for the guinea-pig it was : 

log W = 3-987 log {10 {t - 12)} + 5-1839; 

The significant thing about these empirical formulae is the deduction 
of a certain time in each case from the conception age, thus 7-2 days 
in the case of the mouse, 1 2 days in the case of the guinea-pig, and 
0*5 day in the case of the chick (Allen & McDowell). The evidence 
on which McDowell and his collaborators rested their case for this 
shortening of the development time was drawn from various sources ; 
thus, from their own histological observations they found that the 
primitive streak in the mouse embryo appeared about the 7th day 
of development, for 6-day embryos show no mesoderm, while 7-day 
ones do, and usually the primitive groove as well. Sobotta's work is 
in agreement with this estimate. Their estimate for 12 days as the 
time taken for the embryo guinea-pig to reach the primitive-groove 
stage was based on the generally accepted work of BischoflT and 
Lieberkiihn, while, for the chick, Duval, whose illustrations are the 

SECT. 2] 



usual "normaltafeln", shows the first appearance of the primitive 
groove at the loth hour of development, an assessment which is 
agreed to by Jenkinson and by Foster & Balfour (12th hour). 

Table 53. Probable dimensions of egg-cells. 



in grams 

in fi 








Lamprey ... 





Sturgeon ... 




























Spiny anteater ... 


























Mouse ... 
























Horse ... 



Sheep ... 














Tarsius ... 




Gibbon ... 












"The general course of pre-natal growth in the mouse, the guinea- 
pig and the chick, can be expressed by straight lines relating the 
logarithms of the weight and the age only when age is counted from 
the beginning of the embryo proper." Such is the conclusion of 
McDowell and his collaborators, and, though it may seem barren 



[PT. Ill 

in theoretical results, it is nevertheless based on sounder considerations 
than the more ambitious 
ones of other workers*. It 
is probably legitimate to 
assume that the laws of 
growth before the formation 
of the embryonic axis are 
very different from what 
they are afterwards. It is 
also legitimate to assume 
that the differences between 
the velocity constants in the 
three formulae are due to 
the varying amount of or- 
ganisation which has to go 
on in each case before the ^ 
formation of the primitive < 
groove. Fig. 40 shows the o 
straight-line relationships ? 
found to hold by McDowell, ^ 
Allen & McDowell in the 9 
case of the guinea-pig, mouse ^ 
and chick, and Fig. 41 
gives further examples, from 
which further variants of 
McDowell's formulae could 
easily be calculated. Clearly 
in embryonic growth log. 
weight is always propor- 
tional to log. time. 

With respect to Fig. 39, 
in which the weights of very 
young chick embryos are 
given, it should be noted 
that the discrepancy would 
naturally be expected to 
occur only in the early 
stages, for in the later ones the difference between conception age 
and embryo age would be a smaller percentage of the total. The 

* But see p. 427. 


• n 






1 o- ono 


I 9 • 

/ 7 

> '-A 




// / 


// /i! 


'■il P- 


7 VI' 



. L 

/ i 







// ' 

/ i 

/ / 


f UJ 

ho J 





























2 4 10 20 4060100 200 400 600 

Fig. 40. 


averages for the early embryos reveal the difference by bending away 
from the lines drawn on the basis of incubation or conception age. 

Schmalhausen, continuing earlier work on the growth of bacilli and 
protozoa, has also put forward empirical formulae for the embryonic 
growth of the chick, but his equation 

\^W= T, 

while fundamentally the same as that of Murray, has no velocity 
constant. Fig. 42, taken from Schmalhausen's paper, shows that 
the cube root of the weight plotted against the age only gives an 
approximately straight line. Schmalhausen has included in the same 
figure the curves obtained by other methods; thus curve P' is the 
Minot (percentage growth-rate) curve for the wet weight, and Ps' 
for dry weight, while the curve marked log o- ip is the log. weight 
plotted against the age. As we have already seen, in the case of 
McDowell's figures for the mouse, and Murray's figures for the chick, 
this value always gives a curve rising concave to the abscissa. The 
curves P and Ps in Fig. 42 represent the absolute wet and dry weights 

Other empirical formulae have been proposed for growth-pro- 
cesses from time to time. 

Embryonic growth can be expressed roughly by exponential curves ; 

W = wp\ 

where W is the mass of the embryo at time t, w the original mass, 
and p a constant. Thus the equation of an exponential curve is one 
in which the power is always changing. Janisch has given a dis- 
cussion of the use of the exponential curve in all departments of 
biology, and in it he shows how important this relation is in growth 

The "law of compound interest "however, put forward byBlackman 
in 1919 for the growth of plants, and which has been shown by 
Luyet to be a special form of the exponential relation 

W= w {i + ry, 

has not so far been of any assistance in describing embryonic growth. 
Another form of the exponential curve, the arithmetical progression 
method, which gives the equation 

log W - At, 



[PT. Ill 

where A is 3. characteristic constant, was used by Faure-Fremiet in 
1922 for describing the growth of a Vorticella colony, but the con- 



Hasselbalch 1900 
O Series (a) 
D « (h) 

Bohr& Hasselbalch 1900 
• LamsonS^Edmond 1914 

Ijin 1917 
O LeBrebon8(Schaeffer1923 
B Murray 1926 

Schmalhausen 1926 
^ Needham 1927 


Stobsenberg 1915 

® McDowell etc. 1927 
<§> LeBreton&Schaeffer1923 

O Draper 1920 

® Colin 1888 

O LeBrebon&.Scliaeffer1923 
O Warwick 1928 

X Scheminski 1922 

O Chaine 1911 
« Lochhead&,Cramer1908 


1 00 days 

Fig. 41. 

ditions there are too far removed from those of embryonic develop- 
ment to make it worth while considering this aspect of the subject 
in detail. The formula proposed by Faure-Fremiet for the growth 

SECT. 2] 



of the epithelium of the foetal lung is, however, of greater 

interest i 

W = At^w + Bfiw + Ctw + Dw, 

where w is the total weight of the lung at the time in question. But 
here the number of arbitrary constants is so large that we reach the 
point where the question naturally arises whether an empirical 

/q^ 0,1 p 

7 8 3 10 i1 12 13 1'^■ 15 16 17 18 19 20 21 
Fig. 42. 

formula is worth looking for at all. The more complicated it is, 
the less valuable it is, in view of the fact that, in any case, it is 
not intended to give us an idea of the basic factors underlying the 

2-5. Percentage Growth-rate and the Mitotic Index 

We have so far been examining the results of those investigators 
who have taken the curves obtained by simply plotting the weight 
of the embryo each day during development against the time, and 
who have endeavoured to find a correct mathematical expression 
for them without a preconceived theory. We have now to consider 

400 ON INCREASE IN SIZE [pt. iii 

the work of those who have infused more theory into their treatment 
of the experimental facts. 

Before 1890 there was no regularity in the way in which experi- 
mentalists examined their data on growth. But about that time 
Minot began a long series of investigations on the growth of 
animals, mainly the guinea-pig and the rat, in which he introduced 
a new method, namely, the evaluation of the growth-rate by taking 
it as the increment in per cent, of the weight of the animal at the 
beginning of the period in question. Some workers, e.g. Preyer, had 
already adopted this plan. The percentage growth-rate has always 
been found to decline enormously as development proceeds, an 
observation which led Minot to say that the embryo gets oldest 
most quickly when it is youngest. This apparently paradoxical 
statement drew a good deal of attention to his work at the time, and 
his book. The Problem of Age, Growth, and Death, included many such 
graphs showing how rate of senescence was greatest in the earliest 
periods. One of these is reproduced here as Fig. 43. 

Another contribution of Minot's was the conception of the "mitotic 
index", or the number of mitosing cells per 1000 cells in a tissue. 
He did not himself find time to do more than a few of these laborious 
counts, but he gave the following figures, which showed that the 
mitotic index declined with age: 

Development of 
rabbit foetus (days) Tissue 

Mitotic index 


















Spinal cord 
Connective tissue 






Excretory tissue 


These data lent weight to his principal conclusion, which was that 
the younger the embryo the more rapidly it aged. Practically 
nothing more was done along these lines until Olivo & Slavich in 
1929 reported a large series of figures for the mitotic index of the 
developing heart in the chick. 

SECT. 2] 





period in 






38 minu 














1 1 










































10 (after hatching) 



The fall in the mitotic index ran closely parallel with the fall in the 
percentage growth-rate of the organ, as determined by a special 
series of weighings. The time taken by one mitosis was calculated 
from these data by Olivo & Slavich : it turned out to be constant at 
38 minutes. But the intermitotic period grew longer and longer, 
indicating that the later growth consists less than the former of 
proliferation and more of increase in size of the cells already formed. 


( Males ] 

Z 5 811 17 23 29 3S3« 45 

75 80 105 120 135 150 165 180 185 210 dstye 241 

Fig- 43- 

For a long time Minot's way of looking at embryonic growth in par- 
ticular and growth in general was universally adopted, e.g. by 
Jenkinson, and even at the present time it is much used. But the 
Minot curve is undoubtedly based on a fallacy, and it was not long 
before a feeling that this was so began to arise. It was perhaps 
intensified by the appearance of such estimates as that of 
Muhlmann, who worked out the growth-rates in early stages of 

N E I . 26 

402 ON INCREASE IN SIZE [pt. iii 

embryonic development in man as 3650 per cent, and above. It 
was not unnatural to enquire whether the Minot growth-rate of the 
original dividing egg-cell was even finite. 

The dissatisfaction was voiced in 191 7 by d'Arcy Thompson, who 
wrote as follows: "It was apparently from a feeling that the velocity 
of growth ought in some way to be equated with the mass of the 
growing structure that Minot introduced a curious and (as it seems 
to me) an unhappy method of representing growth in the form of 
what he called 'percentage-curves'. Now when we plot actual length 
against time we have a perfectly definite thing. When we differentiate 
this LjT we have dLjdT which is of course velocity, and from this 
by a second differentiation we obtain d^LjdT^, that is to say, the 
acceleration. But when you take percentages of jv, you are deter- 
mining dyly and when you plot this against dx you have —-^ or 


— ^ or - . ^ , that is to say, you are multiplying the thing you wish 
y.dx y dx 

to represent by another quantity which is itself continually varying, 
and the result is that you are dealing with something very much less 
easily grasped by the mind than the original factors. Minot is of 
course dealing with a perfectly legitimate function of x and y and 
his method is practically tantamount to plotting logy against x^ 
that is to say, the logarithm of the increment against the time. [Cf. 
log. weight-age curves.] This could only be defended and justified if it 
led to some simple result, lOr instance if it gave us a straight line, or 
some other simpler curve than our usual curves of growth". This 
criticism was justified, for the Minot curve is certainly no simpler 
than the untouched growth curves ; it merely falls instead of rising. 

But d'Arcy Thompson did not point out the presence of a 
definite fallacy in Minot's way of looking at growth, a physio- 
logical rather than a mathematical one. This was grasped by Brody, 
who has written as follows: "Minot's method for computing growth- 
rates gives an exaggerated decline in the percentage rates of growth 
with increasing age simply because an arbitrary unit of time, e.g. 
a week, does not have the same significance at different ages. It is, 
for example, entirely appropriate to express the gain in weight during 
a week as a percentage of the weight at the beginning of the week 
(Minot's method) for a 6-month old chicken, because the weights 
(i.e. the number of cells or other reproducing units) at the beginning 


and end of the week are nearly the same as compared to the gain in 
weight. But to express the gain in weight during a week as a per- 
centage of the weight of the body at the beginning of the week for 
a 7-day old chick embryo would be quite fallacious. It would cor- 
respond to expressing the gain in population in the U.S.A. from 1666 
to 1927 as a percentage of the size of the population in 1666. The 
growth of the population of the U.S.A. in 1927 is proportional to the 
population in 1927 and not to the population in 1666. Similarly the 
number of cells produced in a 7-day old chick embryo should be 
functionally related to the number of reproducing cells (i.e. the 
weight) of the chick at 7 days of age and not to the number of cells 
at I day of age. In brief, growth is a continuous process and the 
rate of growth at every instant should be functionally related to 
the number of reproducing units at the given instant and not to 
the number of reproducing units which existed in some relatively 
remote past". In other words, Brody would prefer to ask not how 
much 100 gm. of embryo add on to themselves during the im- 
mediately succeeding period, but rather how many grams of those 
1 00 gm. had been added on during a short preceding period. Murray's 
modification of Minot's method, in which the mid-increments in- 
stead of the daily increments are used as the basis for calculation, 
goes some way to meet Brody's criticism, for it enquires how much 
100 gm. of embryo add on to themselves during half the preceding 
and half the following period, thus speaking in terms of a more 
instantaneous measure. Brody himself has made use of a similar 
amelioration. However, Brody's real point is that the fault lies in 
choosing an arbitrary length of time interval for all stages of develop- 
ment, in spite of the fact that they cannot possibly be equivalent for 
the embryo. 

Brody might say that the embryo cannot be regarded as having 
been given an equal chance to accomplish its growth in each of the 
daily periods throughout its development. On the other hand, it 
might be argued that, though this is doubtless true as regards growth 
in weight, it is not true with respect to the activities of the embryo 
as a whole, which include many other processes, such as chemical 
differentiation. Taking the embryo as a whole in all its activities, 
the arbitrarily chosen and invariant period might be regarded as an 
adequate one. As we shall see later, this is essentially the same 
argument as that used by Murray against Robertson. 




[PT. Ill 

It may, however, be concluded that the Minot curve is only useful 
provided no theoretical conclusions are drawn from it, and that it 
is retained simply as a convenient method of comparing processes. 
Brody's own theories will be discussed later. 

As against the theory which Minot built up from his experiments 
with growing animals, Murray has brought forward one convincing 

-0.15 1 

n 4 «. 













• -0.05 














5 6 7 8 9 10 tl 12 13 14 15 16 17 IS 19 ^ 



argument. Minot's theory of cytomorphosis involved the following 
propositions: (i) that the rate of growth depends on the degree of 
senescence, (2) that senescence is at its maximum when development 
begins, (3) that the rate of senescence decreases with age, and (4) that 
death results from the differentiation of cells. But, as Murray says, 
we have no real evidence to show us that the "degree of aliveness" 
at any given moment is in any way connected with the velocity of 
growth at that particular moment, or, more correctly, that the latter 


value is a true measure of the former, "There are other and perhaps 
more significant phenomena", said Murray, "than the growth rate, 
which change with age." 

Murray himself proposed the use of a variant of the usual Minot 
curve by differentiating twice instead of once so as to get the ac- 
celeration and not the velocity. Thus, after having found the per- 
centage growth-rate by the equation 

dt[_w\ t' 

where K ^ 3-6, he went on to find the negative acceleration for each 
day during embryonic growth : 




= - Kt^. 

This value, so obtained, is, as it were, the negative increment of 
the percentage growth-rate, and shows a regularly declining curve 
(for the chick) as in Fig. 44. Such a curve must obviously suffer 
from the same disadvantages as the curve from which it is derived, 
and does not escape from Brody's criticism that the arbitrarily 
chosen time-units are incommensurable at different developmental 

In 1922 Przibram observed that in many cases of post-embryonic 
growth the curve obtained by calculating according to Minot's 
method was extremely like a regular hyperbola, but he did not find 
that this was true for any example of embryonic growth. We shall 
see later what further use of this idea has been made, 

2-6. Yolk Absorption-rate 

Another way of regarding embryonic growth (of a lecithic Ggg) 
is to concentrate attention on the whole system, instead of upon 
the growth of the embryo alone. It was in this way that Gray 
treated the development of the trout embryo in the paper already 
mentioned (p. 369 and Appendix i). He assumed that the rate of 
growth of the embryo was proportional to the dry weight of the 
embryo and to the dry weight of the remaining yolk. This idea had 
already been introduced for the trout by Kronfeld & Scheminzki 
(see p. 369 and Fig. 41) but Gray's figures were much more complete, 
and showed very clearly a falling off of growth towards the end of 

4o6 ON INCREASE IN SIZE [pt. iii 

pre-natal life, when the yolk was becoming exhausted. Thus the wet 
weight of an embryo plotted against the time gave an S-shaped 
curve, which, however, was not symmetrical, for it had a point of 
inflection after about 70 per cent, instead of 50 per cent, of the 
development had been completed. This was of course well shown on 
the increment curve, which was skewly bell-shaped. Assuming that 
growth was proportional to the amount of yolk remaining as well 
as to the size of the embryo already formed, Gray developed an 
equation ^ 

(where x is the weight of the embryo at time t,yQ the total yolk in 
the unfertilised egg, K^, the amount of yolk combusted by one gram 
of embryo divided by the constant k in the equation 

dx J 

It = '"^' 

X and y being weight of embryo and weight of yolk respectively) 
which he considered accounted very well for the observed facts. He 
deduced from it that there should be a period at the end of develop- 
ment when the wet weight of the larva (the whole system, embryo 
plus yolk) is decreasing, although the wet weight of the embryo itself 
is still increasing. During the major part of development the wet 
weight of both would increase, owing to the absorption of water 
from outside. From the equations the maximum weight of the larva 
should be reached when o-86 gm. of yolk is still unconsumed, and 
in actual fact Gray found the peak at a point when i*io gm. \^as 
yet remaining. 

Another possibility used by Gray to test his hypothesis was that 
as it was unlikely that the temperature coefficient of the growth 
process would be the same as that of the catabolism going on, there 
ought to be a measurable difference in the size of fishes raised at 
various temperatures at the end of their development. Experiments 
designed to reveal such differences gave the following results : 

Mean weight of 100 embryos at 
Temperature (°C.) the end of incubation (gm.) 

15 i3-35±o-i6 

ID i507±o-i8 

so that the higher temperature not only accelerated the process, but, 
by accelerating the combustion more than the storage, led to a 

SECT. 2] 



smaller finished fish. These results are curious, for it is generally- 
understood that temperature changes alter the rate at which a 
growth-process goes on yet not the amount of end-product formed. 
The work of Barthelemy & Bonnet on the frog is an exact parallel 
to that of Gra